St. Paul says in the letter to the Romans, “I can will what is right, but I cannot do it. For I do not do the good I want, but the evil I do not want is what I do.”
This happens because the person is divided. Simply speaking I may believe that the thing that I want to do is right; but in another way, I perceive or suppose that “the evil I do not want” is good.
This sort of division can happen in the opposite way as well, so that a person wills the evil that he takes to be good, but cannot do it, because another part of him perceives that it is evil and to be avoided.
Procrastination can work as an example of both cases. Without a doubt procrastinating is often failing to do the good that one wills; but it is also often refusing to do something that would be mostly pointless, and in this sense, it is refusing to do something bad, and thus one could say that “I do not the evil I want, but the good I do not want is what I do.”