We do things because we are weak.
We sometimes feel that if we would have just more energy and will power we would have done X and Y and Z. This and this and this would have been different.
But many times what we call weakness is in a sense a wisdom of our gut feeling. We may lose because of weakness, but we win many times out of weakness. Being strong willed may mean suffering too much for useless or unrealistic goals. At times, the goals are not worth the trouble. Our smartness says it is. But weakness of will, saves us from being zealous toward the unworthy of effort.
Our "well thought out goals" are many times grudging efforts to acheive goals that are coming not so much from wisdom but form other people's interests, all kinds of psychological constructs and so on. Failing may mean avoiding throwing energy away. 
Considering weakness when managing life
Realistically, it does not always matter what would have happened if we would have acted with stronger will. Our weakness and and idiosyncraticas, are there to be taken into consideration.
True, we have some power to change at times. But many times we do not. Even if we can in theory, we may be the kind of person who usually does not exercise such a strong will power.
For regular management of life, it may be wise to take our usual will power into account.
Generally, maanging life out of theoretical possibilities or of our teachers of strong people is not smart. We manage life by our own means and tendencies.
 Randolph Nesse claims here that the evolutionary source of depression is either to make us able to sumbit to those stronger of us, or to abandom unfeasible goals.
PS. scholars have shown that having generally more self-regulation ability helps in various domains of life. Self-regulation capacity can actually be increases by exercising in self-regulation. But it does not always work.
These scholastic works, makes me feeling strange about this post. I certainly have my points. But do I give them too much emphasis because I want to believe in these aspects of being weak?