What causes a stock to drop in price?
A rising tide lifts all ships   Most (but not all) stocks trend along with the general market. Some trend right along with the market (and have a beta at, or very near, one) some follow the Market, but are less sensitive (having a beta of less than one). Some are hypersensitive (and would have a beta of greater than one).  Beta defined  So most of the day to day movement of a stock is because the general market is moving (in the same direction). Of course, exceptional news about the company would cause its price to move independent of the general market. But more often than not the price of a stock moves just because the rest of the market is moving.
Any time a large order it placed for Buy, the sell side starts increasing as the demand of Buy has gone up. [Vice Versa is also true]. Once this orders gets fulfilled, the demand drops and hence the Sell price should also lower. Depending on how much was the demand / supply without your order, the price fluctuation would vary. For examply if before your order, for this particular share the normal volume is around 100's of shares then you order would spike things up quite a bit. However if for other share the normal volume is around 100000's then your order would not have much impact. The 'normal' series of events when trading a stock is to buy it, time passes, then you sell it. If you believe the stock will drop in price, you can reverse the order, selling shares, waiting for the price drop, then buying them back. During that time you own say, -100 shares, and are 'short' those shares. "Both explanations are partly true. There are many investors who do not want to sell an asset at a loss.  This causes ""resistance"" at prices where large amounts of the asset were previously traded by such investors.  It also explains why a ""break-through"" of such a ""resistance"" is often associated with a substantial ""move"" in price. There are also many investors who have ""stop-loss"" or ""trailing stop-loss"" ""limit orders"" in effect.  These investors will automatically sell out of a long position (or buy out of a short position) if the price drops (or rises) by a certain percentage (typically 8% - 10%). There are periods of time when money is flowing into an asset or asset class.  This could be due to a large investor trying to quietly purchase the asset in a way that avoids raising the price earlier than necessary.  Or perhaps a large investor is dollar-cost-averaging.  Or perhaps a legal mandate for a category of investors has changed, and they need to rebalance their portfolios.  This rebalancing is likely to take place over time.  Or perhaps there is a fad where many small investors (at various times) decide to increase (or decrease) their stake in an asset class.  Or perhaps (for demographic reasons) the number of investors in a particular situation is increasing, so there are more investors who want to make particular investments.  All of these phenomena can be summarized by the word ""momentum"". Traders who use technical analysis (including most day traders and algorithmic speculators) are aware of these phenomena.  They are therefore more likely to purchase (or sell, or short) an asset shortly after one of their ""buy signals"" or ""sell signals"" is triggered.  This reinforces the phenomena. There are also poorly-understood long-term cycles that affect business fundamentals and/or the politics that constrain business activity.  For example: Note that even if the markets really were a random walk, it would still be profitable (and risk-reducing) to perform dollar-cost-averaging when buying into a position, and also perform averaging when selling out of a position.  But this means that recent investor behavior can be used to predict the near-future behavior of investors, which justifies technical analysis." There are many things that can make a company's share price go up or down. Generally, over the long term, the more consistently profitable a company is the more its share price will go up. However, there are times when a company may not be making any profits yet but its share price still goes up. This can be due to forecasts that the company will start making profits in the near future. Sometimes a company may report increased profits from the previous year but makes less than what the market was expecting it to make. This can cause its share price to fall, as the market is disappointed in the results. In the shorter term greed, fear and speculation can make a company's share price move irrationally. When you think the share price should be going up it suddenly falls, and Vis-versa. When interest rates are low, companies with higher dividend yields (compared to bank account interest rates) become high in demand and their shares generally go up in price. As the share price goes up the dividend yield will be reduced unless the company continues to increase the dividend it distributes to shareholders. When interest rates start to rise these companies become less favourable as they are seen as higher risk comparable to similar returns from having one's money in the safety of the bank. This can cause the share prices to fall. These are just some of the reasons that make a company's share price move up or down. As humans are an irrational bunch often ruled by emotions, sometimes the reasons share prices move in a particular direction can be quite confusing, but that is the nature of the financial markets. You may simply be asking why stocks 'gap up' or 'gap down' when the stock market opens. This is because the price adjusts to news that occurred while the exchanges were closed overnight. Perhaps Asian stocks crashed, or perhaps a news story was released in the New York Times about some major company. There are thousands of factors that affect market sentiment, and the big gaps that happen at the open of every trading day is the price of the stocks catching up to those factors. 1) Explicitly, how a company's share price in the secondary market affects the company's operations. (Simply: How does it matter to a company that its share price drops?) I have a vague idea of the answer, but I'd like to see someone cover it in detail.  2) Negative yield curves, or bonds/bills with negative yields  Thanks! "It is important to first understand that true causation of share price may not relate to historical correlation. Just like with scientific experiments, correlation does not imply causation. But we use stock price correlation to attempt to infer causation, where it is reasonable to do so. And to do that you need to understand that prices change for many reasons; some company specific, some industry specific, some market specific. Companies in the same industry may correlate when that industry goes up or down; companies with the same market may correlate when that market goes up or down. In general, in most industries, it is reasonable to assume that competitor companies have stocks which strongly correlate (positively) with each-other to the extent that they do the same thing.  For a simple example, consider three resource companies: ""Oil Ltd."" [100% of its assets relate to Oil]; ""Oil and Iron Inc."" [50% of its value relates to Oil, 50% to Iron]; and ""Iron and Copper Ltd."" [50% of its value relates to Iron, 50% to Copper]. For each of these companies, there are many things which affect value, but one could naively simplify things by saying ""value of a resource company is defined by the expected future volume of goods mined/drilled * the expected resource price, less all fixed and variable costs"". So, one major thing that impacts resource companies is simply the current & projected price of those resources. This means that if the price of Oil goes up or down, it will partially affect the value of the two Oil companies above - but how much it affects each company will depend on the volume of Oil it drills, and the timeline that it expects to get that Oil. For example, maybe Oil and Iron Ltd. has no currently producing Oil rigs, but it has just made massive investments which expect to drill Oil in 2 years - and the market expects Oil prices to return to a high value in 2 years.  In that case, a drop in Oil would impact Oil Inc. severely, but perhaps it wouldn't impact Oil and Iron Ltd. as much. In this case, for the particular share price movement related to the price of Oil, the two companies would not be correlated. Iron and Copper Ltd. would be unaffected by the price of Oil [this is a simplification; Oil prices impact many areas of the economy], and therefore there would be no correlation at all between this company's shares. It is also likely that competitors face similar markets. If consumer spending goes down, then perhaps the stock of most consumer product companies would go down as well. There would be outliers, because specific companies may still succeed in a falling market, but in generally, there would be a lot of correlation between two companies with the same market.  In the case that you list, Sony vs Samsung, there would be some factors that correlate positively, and some that correlate negatively. A clean example would be Blackberry stock vs Apple stock - because Apple's success had specifically negative ramifications for Blackberry. And yet, other tech company competitors also succeeded in the same time period, meaning they did not correlate negatively with Apple." Here are some significant factors affect the company stock price performance: Usually, profitability is known to the public through the financial statements; it won't be 100% accurate and people would also trade the stock with the price not matching to the true value of the firm. Still there are dozens of other various reasons exist. People are just not behaving as rational as what the textbook describes when they are trading and investing. It's the buying and selling of the stock that causes the fluctuation in prices, not the news. People buy and sell all the time, and not just for newsworthy reasons.  They may have to send a child to college, or fix a roof, etc.  Or they may be technical traders looking for signals.  All kinds of reasons. You would think that share prices is just a reflection of how well the company is doing but that is not always the case. Sometimes it reflects the investor confidence in the company more than the mere performance. So for instance if some oil company causes some natural disaster by letting one of there oil tankers crash into a coral reef then investor confidence my take a big hit and share prices my fall even if the bottom line of the company was not all that effected. This can arise with very thinly traded stocks for large blocks of shares. If the market only has a few thousand dollars available at between 8.37 and 12.5 the price is largely meaningless for people who want to invest in hundreds of thousands/millions of dollars worth, as the quoted price can't get them anywhere near the number of shares they want. How liquid is the stock in question? You are misunderstanding what makes the price of a stock go up and down. Every time you sell a share of a stock, there is someone else that buys the stock.  So it is not accurate to say that stock prices go down when large amounts of the stock are sold, and up when large amounts of the stock are bought.  Every day, the amount of shares of a stock that are bought and sold are equal to each other, because in order to sell a share of stock, someone has to buy it. Let me try to explain what actually happens to the price of a stock when you want to sell it. Let's say that a particular stock is listed on the ticker at $100 a share currently.  All this means is that the last transaction that took place was for $100; someone sold their share to a buyer for $100. Now let's say that you have a share of the stock you'd like to sell.  You are hoping to get $100 for your share.  There are 2 other people that also have a share that they want to sell.  However, there is only 1 person that wants to buy a share of stock, and he only wants to pay $99 for a share.  If none of you wants to sell lower than $100, then no shares get sold.  But if one of you agrees to sell at $99, then the sale takes place.  The ticker value of the stock is now $99 instead of $100. Now let's say that there are 3 new people that have decided they want to buy a share of the stock.  They'd like to buy at $99, but you and the other person left with a share want to sell at $100.  Either one of the sellers will come down to $99 or one of the buyers will go up to $100.  This process will continue until everyone that wants to sell a share has sold, and everyone who wants to buy a share has bought.  In general, though, when there are more people that want to sell than buy, the price goes down, and when there are more people that want to buy than sell, the price goes up. To answer your question, if your selling of the stock had caused the price to go down, it means that you would have gotten less money for your stock than if it had not gone down.  Likewise, if your buying the stock had caused it to go up, it just means that it would have cost you more to buy the stock.  It is just as likely that you would lose money doing this, rather than gain money. The company may have put a trading halt due to many reasons, most of the time it is because the company is about to release some news to the market. To stop speculation driving the price up or down, it puts a halt on trading until it can get all the information together and release it to the market. This could be news about an earnings update, a purchase of other businesses, a merger with another business, or a takeover bid, just to name a few. "The simple answer could be that one or more ""people"" decided to buy. By ""people,"" I don't mean individual buyers of 100 shares like you or me, but typically large institutional investors like Fidelity, who might buy millions of shares at a time. Or if you're talking about a human person, perhaps someone like Warren Buffett. In a ""thinly"" traded small cap stock that typically trades a few hundred shares in a day, an order for ""thousands"" could significantly move the price. This is one situation where more or less ""average"" people could move a single stock." Just playing devil's advocate: A falling stock price impairs the firm's ability to raise equity capital efficiently. In these times, additional regulatory capital requirements continue to be levied on the banks, and they are faced with raising capital inefficiently, which may impair their ability to pay their debt, which may lead to a ratings downgrade.