Because once it is accepted, the fact that life is difficult no longer matters. Most do not fully see this truth that life is difficult. Instead they moan more or less incessantly, noisily or subtly, about the enormity of their problems, their burdens, and their difficulties as if life were generally easy, as if life should be easy. They voice their belief, noisily or subtly, that their difficulties represent a unique kind of affliction that should not be and that has somehow been specially visited upon them, or else upon their families, their tribe, their class, their nation, their race or even their species, and not upon others. I know about this moaning because I have done my share.
Life is a series of problems.
Discipline is the basic set of tools we require to solve life's problems. Without discipline we can solve nothing. With only some discipline we can solve only some problems. With total discipline we can solve all problems. It is for this reason that wise people learn not to dread but actually to welcome problems and actually to welcome the pain of problems.