Because we all know what will go down, we'll desire so much from people, situations and moments that we miss the whole point of living it. It's not like we shouldn't have dreams or expectations, it's just that when reality kicks in, it's better to let things flow than increase the "awesomeness" of the idea in our head.
Plus, as always, pop culture, movies and songs get a big slice of the guilt pie. We're supposed to believe to find love in the darnest situations, to change ourselves so we can be more accepted and, when you are in a crossroad, you're bound to have a special revealing moment that helps you solve all of your problems until that point. Guess what? There is no such moment.
I won't say anything about love or changes, because that has a better chance of happening, but this doesn't. You won't be sitting on a train to leave home and realize that you should stay, first of all you probably wouldn't even hop on the train or you would've arrived to your new destination just to confirm the fact that you hate that place and want to go back.
Revelations or epiphanies won't occur in the climax point of your own life movie, just when you need it, because they come from within. They're answers inside of you that didn't realized you were asking a question.
Don't go around life expecting to have a ground breaking spiritual moment in a mystical place, because inner questions can be answered during a silent moment and the only revelation about life you will acknowledge is the one that comes from you.