In truth, your best purchases will be the times that you are almost crapping your pants in fear....a stock has been hammered down, but not without reason.  And you are buying it because you think that the "reason" will go away with time and/or the market has waaaay over-reacted to a near term issue.

In fact, when you make that purchase, you probably don't actually have all that much "conviction", but you are sticking with your discipline, and buying what looks like a very, very inexpensive business.  And you close your eyes, and promise to not open them for at least 18 months.....