Which is why you need as many good ones as possible.
I already totally destroyed this thinking a few years ago. There's a limited number of good, young prospects out there, so if you're trying to stockpile enough to fill up a good ML roster some day, you're playing a loser's game.
If a team offers you a solid MLB player for four prospects, each with a 1/5 chance of becoming just as good as that MLB player, you should take that MLB player, even if there's some very small chance of one of them becoming really good.