Could ignoring sunk costs be used to make an investment look more attractive when it's really not?
I'm not sure that you're considering all the options.   So you may not subtract $X from B, but you do compare NPV(B) to $Y.   Also, remember that we're not trying to figure out the return on B.  We're trying to figure out what to do next.  In terms of planning, the sunk cost is irrelevant.  But in terms of calculating return, A was a turkey.  And to calculate the return, we would include $X in our costs for B.  And for the second option, we'd subtract $X from $Y (may be negative).   Sunk costs are irrelevant to planning, but they are very relevant to retrospective analysis.  Please don't confuse the two.  When looking back, part of the cost for B will be that $X.  But in the middle, after paying $X and before starting B, the $X is gone.  You only have the building and have to make your decision based on the options you have at that moment.   You will sometimes hear $Y called the opportunity cost of B.  You could sell out for $Y or you could do B.  You should only do B if it is worth more than $Y.   The sunk cost fallacy would be comparing B to $X.  Assuming $Y is less than $X, this would make you not do B when it is your best path forward from that moment.  I.e. $Y < NPV(B) < $X means that you should do the project.  You will lose money (apparently that's a foregone conclusion), but you will lose less money than if you just sold out.   You should also do B if $Y < $X < NPV(B) or $X < $Y < NPV(B).  In general, you should do B any time $Y < NPV(B).  The only time you should not do B is if NPV(B) < $Y.  If they are exactly equal, then it doesn't matter financially whether you do B or not.
Keep in mind there are a couple of points to ponder here: Rates are really low. With rates being so low, unless there is deflation, it is pretty easy to see even moderate inflation of 1-2% being enough to eat the yield completely which would be why the returns are negative. Inflation is still relatively contained. With inflation low, there is no reason for the central banks to raise rates which would give new bonds a better rate. Thus, this changes in CPI are still in the range where central banks want to be stimulative with their policy which means rates are low which if lower than inflation rates would give a negative real return which would be seen as a way to trigger more spending since putting the money into treasury debt will lose money to inflation in terms of purchasing power. A good question to ponder is has this happened before in the history of the world and what could we learn from that point in time. The idea for investors would be to find alternative holdings for their cash and bonds if they want to beat inflation though there are some inflation-indexed bonds that aren't likely appearing in the chart that could also be something to add to the picture here. "In economics, there is a notion called the Sunk Cost Fallacy.  In a nutshell, the sunk cost fallacy says that human beings tend to prefer to ""throw good money after bad"" because of a strong loss aversion.  That, coupled with how we frame an issue, makes it very tempting to say, ""if I just add these funds, I'll recoup my loss plus..."" In reality, the best best is to ignore sunk costs.  (I know, far easier said than done, but bear with me a second.)  How much you've invested is really irrelevant.  The only question worth asking is this: ""Would I invest this money in the asset today?"" Put it this way - any money you spend on ""rescuing"" this upside mortgage is an investment that trades ready funds for a little more equity.  Knowing that the mortgage is $100K in excess of the value, why buy that asset?  If you could do a HARP, different story - but as you say, you can't. As such, buying into that investment is not the best use of your funds. You are throwing good money after bad.  Invest your money where it will earn the best rate of return - not where your heart lead you." If your gut told you to buy during the depths of '09, your gut might be well-calibrated. The problem is stock market declines during recessions are frequently not that large relative to the average long run return of 9%:  A better strategy might be hold a percentage in equities based upon a probability distribution of historical returns.  This becomes problematic because of changes in the definition of earnings and the recent inflation stability which has encouraged high valuations:  Cash flow has not been as corrupted as earnings now, and might be a better indicator:  This obviously isn't perfect either, but returns can be improved. Since there is no formulaic way yet conventionally available, the optimal primary strategy is still buy & hold which has made the most successful investor frequently one of the richest people on the planet for decades, but this could still be used as an auxiliary for cash management reserves during recessions once retired. "A big part of the answer depends on how ""beaten down"" the stock is, how long it will take to recover from the drop, and your taste for risk. If you honestly believe the drop is a temporary aberration then averaging down can be a good strategy to lower your dollar-cost average in the stock.  But this is a huge risk if you're wrong, because now you're going to magnify your losses by piling on more stock that isn't going anywhere to the shares you already own at a higher cost. As @Mindwin pointed out correctly, the problem for most investors following an ""average down"" strategy is that it makes them much less likely to cut their losses when the stock doesn't recover.  They basically become ""married"" to the stock because they've actualized their belief the stock will bounce back when maybe it never will or worse, drops even more." "There are obviously lots of complexities here, and there are rules against price or market manipulation that are somewhat interpretive due to the rules' inclusion of the manipulator's intent, but: Generally speaking, you can publicly promote the value of a company whose stock you own provided that you: Now, if you extol the value of a company publicly, and sell it immediately thereafter, ""pump and dump,"" the regulators might suggest that your actions imply that you didn't believe it was so wonderful, and were misleading the public to move the price.     That said, a fair retort might be that you loved it for all the reasons you said at [lower price], but thought it had run its course once it got to [higher price].   Again, if it can be demonstrated that your reason for praising it was to push the price higher, your intent may land you in hot water. This isn't legal advice or a full analysis, but if Fitty essentially declared his honest reasons for loving a stock in which he is invested, and discloses that investment, letting others know he is biased, he's probably ok, especially if he intends to hold it long term." "The root of the advice Bob is being given is from the premise that the market is temporarily down.    If the market is temporarily down, then the stocks in ""Fund #1"" are on-sale and likely to go up soon (soon is very subjective).     If the market is going to go up soon (again subjective) you are probably better in fictitious Fund #1.    This is the valid logic that is being used by the rep.   I don't think this is manipulative based on costs.    It's really up to Bob whether he agrees with that logic or if he disagrees with that logic and to make his own decision based on that. If this were my account, I would make the decision on where to withdraw based on my target asset allocation. Bob (for good or bad reasons) decided on 2/3 Fund 1 and 1/3 Fund 2. I'd make the withdraw that returns me to my target allocation of 2/3 Fund 1 and 1/3 Fund 2. Depending on performance and contributions, that might be selling Fund 1, selling Fund 2, or selling some of both." "I have heard that investing more money into an investment which has   gone down is generally a bad idea*. ""Throwing good money after bad"" so   to speak. Is investing more money into a stock, you already have a stake in,   which has gone up in price; a good idea? Other things being equal, deciding whether to buy more stocks or shares in a company you're already invested in should be made in the same way you would evaluate any investment decision and -- broadly speaking -- should not be influenced by whether an existing holding has gone up or down in value. For instance, given the current price of the stock, prevailing market conditions, and knowledge about the company, if you think there is a reasonable chance that the price will rise in the time-period you are interested in, then you may want to buy (more) stock. If you think there is a reasonable chance the price will fall, then you probably won't want to buy (more) stock. Note: it may be that the past performance of a company is factored into your decision to buy (e.g was a recent downturn merely a ""blip"", and long-term prospects remain good; or have recent steady rises exhausted the potential for growth for the time being). And while this past performance will have played a part in whether any existing holding went up or down in value, it should only be the past performance -- not whether or not you've gained or lost money -- that affects the new decision. For instance: let us suppose (for reasons that seemed valid at the time) you bought your original holding at £10/share, the price has dropped to £2/share, but you (now) believe both prices were/are ""wrong"" and that the ""true price"" should be around £5/share. If you feel there is a good chance of this being achieved then buying shares at £2, anticipating they'll rally to £5, may be sound. But you should be doing this because you think the price will rise to £5, and not because it will offset the loses in your original holding. (You may also want to take stock and evaluate why you thought it a good idea to buy at £10... if you were overly optimistic then, you should probably be asking yourself whether your current decisions (in this or any share) are ""sound""). There is one area where an existing holding does come into play: as both jamesqf and Victor rightly point out, keeping a ""balanced"" portfolio -- without putting ""all your eggs in one basket"" -- is generally sound advice. So when considering the purchase of additional stock in a company you are already invested in, remember to look at the combined total (old and new) when evaluating how the (potential) purchase will affect your overall portfolio." Quick and dirty paper but pretty interesting.. I'm not in Portfolio Management but I probably would have ended up at the modal number as well.   I don't know the subject deeply enough to answer my own question, but is the bias always toward underestimation of variance? Or is that a complex of the way the problem was set up?   Another question I have for those in investment management; Would this impact asset allocation? "I have heard that investing more money into an investment which has gone down is generally a bad idea*. ""Throwing good money after bad"" so to speak. This is over simplified statement to explain the concept. What is essentially says is; Say I hold stocks of XYZ; 100 units worth say USD 1000. This has lost me x% [say 50%]. The general tendency is to buy 100 more units in anticipation / hope that the price will go up. This is incorrect.  However on case to case basis, this maybe the right decisions. On a periodic basis [or whenever you want to invest more money]; say you have USD 1000 and did not have the stock of XYZ, will you buy this at current price and outlook of the company. If the answer is Yes, hold the stock [or buy more], if the answer is no sell the stock at current market price and take the loss. The same applies when the price has appreciated. If you have USD 1000; given the current price and future outlook, will you buy the specific stock. If yes, hold the stock [or buy more], if answer is no sell the stock and book profit. Off-course I have not overlaid the various other considerations when buying stocks like diversification, risk profiles of individual stocks / segments, tax implications etc that are also essential even if you decide to buy or sell specific stock." I'm sorry for adding another answer @MatthewFlaschen but it is too long for a comment. It depends on the situation. Say you buy shares of the Apple Inc. and want to know what is the lost opportunity cost. You need to find out what other opportunities are. In other words what are the other possible types of investments you consider. For example in theory you could try to invest in any company from S&P 500, but is it really possible (I don’t mean investing directly in index) . Are you really capable of researching each company.  So in your case you would consider only a few companies as alternative solutions. Also after different time period each choice may be your lost opportunity cost.  To measure the risk you have to: In conclusion I want to say that my goal was to picture in general how the process looks. Also this is just an exemplary answer. All is about in what finance field you are interested. For example in one field you use Internal Rate of Return and in other Value at Risk. Opportunity cost is to vague to exactly tell how measure its risk of wrong anticipation. It connects in every finance field and in every field you have different ways do deal with it. If you specify your question more, maybe someone will provide a better answer. The fundamental issue with leverage (of any sort, really) is that the amplified downsides are extremely likely to more than cancel out amplified equivalent upsides. Example without using a major swing: 2x leverage on a 5% decline (so a 10% decline).  The 5% decline needs a 5.26% increase to get back level.  However, the 2x leverage needs an 5.55% increase to get back.  So a cycle for the unleveraged returns of -5%, +5.4% would see the unleveraged asset go up by a net +0.13% but 2x leverage would leave you at -0.28%.  Conversely, imagine 0.5x leverage (it's easy to do that: 50% cash allocation): after an underlying -5%, the 0.5x leverage needs only +5.13% to reach par.  This is basically the argument for low volatility funds. Of course, if you can leverage an asset that doesn't go down, then the leverage is great.  And for an asset with an overall positive compound return, a little leverage is probably not going to hurt, simply because there are likely to be enough upsides to cancel out downsides. I feel really uneasy hearing people arguing about how to recalculate an indicator that does not predict anything. yes, the late 2000 financial bubble was a black swan with low probability of ever happening, but lighting can hit the same place twice. "It would be useful to forget about the initial price that you invested - that loss happened, it's over and irreversible, it's a sunk cost; and anchoring on it would only cause you to make worse decisions. Getting ""back"" from a loss is done exactly the same as growing an investment that didn't have such a loss. You have x units of stock that's currently priced $46.5 - that is your blank slate; you need to decide wether you should hold that stock (i.e., if $46.5 is undervalued and likely to increase) or it's likely to fall further and you should sell it.   The decision you make should be exactly the same as if you'd bought it a bit earlier for $40." "I primarily intend to add on to WBT's answer, which is good. It has been shown that ""momentum"" is a very real, tangible factor in stock returns. Stocks that have done well tend to keep doing well; stocks that are doing poorly tend to keep doing poorly. For a long-term value investor, of course fundamental valuation should be your first thing to look at - but as long as you're comfortable with the company's price as compared to its value, you should absolutely hang onto it if it's been going up. The old saying on Wall Street is ""Cut your losses, and let your winners ride."" As WBT said, there may be some tangible emotional benefit to marking your win while you're ahead and not risking that it tanks, but I'd say the odds are in your favor. If an undervalued company starts rising in stock price, maybe that means the market is starting to recognize it for the deal it is. Hang onto it and enjoy the fruits of your research." Like 90% of them pride themselves in making slightly positive returns at times of turmoil. They never mention their returns on up years (8 our of every 10, at a minimum). At times like this when markets are booming they underperform and it's what have you done for me lately time. They'll slightly rebound next downturn, but still terrible investments because of the fees. Even when you take into account the diversification effect of their negative betas.