Nobody can predict the future. In fantasy football all we can do is make guesses and more educated guesses. The object is to keep a high ceiling while minimizing risk. A lot of upside chasers aim more for the high ceiling than minimizing the risk which is a mistake. When you take too many gambles, you're bound to lose some of them.
There are ways to talk yourself in and out of drafting any player. This article examines the players where the gamble just isn't worth it. I will even play devil's advocate for these guys which will basically be what I tell myself if I end up with one of these players that I don't actually want.