The entire ranger school experience can be summed up in two words:
IT SUCKS.
It isn't super hard, but IT SUCKS. You won't be asked to do any one thing that is physically superhuman, but IT SUCKS. The real challenge is in your mind, to not quit, because IT SUCKS. It is no fun to be tired, hungry and dirty (plus cold or hot and wet) for long periods of time. In fact, IT SUCKS.
But after 61 days, you'll never have to do it again.