Discipline is not really a conscious choice since you can enhance it through medication. So if you have the right makeup then you don't need motivation to do things while others can get roughly the same effect by taking Ritalin.
"A choice", i. e. free will, and something that can be changed via medication aren't mutually exclusive. I'd think most people would agree that getting up early is somewhat in your control, but it gets a lot easier if you have an energy drink at 4am.
There's the theory (see the book by Baumeister) that willpower is like a muscle. It can both get tired and be trained. So the right mindset might not be "I will be disciplined today" – because you will fail and feel bad about it as you would fail if you just decided to lift that huge boulder. But if you chose to expend your willpower on something small but challenging, you may be able to train it and, after a while, be able to lift that heavy boulder.
Yes, I was a bit too simplistic in my post. But the point is that a person who builds discipline like a girl builds muscle will be out of the competition no matter what he does. In such cases it is better to focus on other things to circumvent the shortage of discipline, such as finding more motivation etc, in the same way as girls shouldn't do jobs where they have to lift heavy objects.
