According to marines, will power depletion is bs. This is anecdotal, sure, but I believe in momentum. If you have momentum, at some point, you don't want to fail at any will power task, because you are on a winning streak.
There are only so many points in life where it changes direction. Most of the time is doing what you did the past months/years, whatever is staying home getting drunk or working non-stop. Sure you can change direction, but it's not easy to fight inertia. You gotta apply some force to change direction!
Also, if you transform what you want, you reduce need for will power.
Often momentum is kept by NOT taking more difficult decisions.
Also, if you don't trust psychologists you should trust the marines even less.