With that in mind, it's better to forget about the imaginary concept of willpower altogether, and look at reframing things so that different decision making systems come to the fore; or altering factors that are gumming up the decision making process.
The point at the end about stigmatizing people for lacking this imaginary attribute is particularly important. It's political, too; if you curtail people's freedom even in their best interests, it's easy to become corrupted from that position of power. Maintaining a belief in an invented character defect is a convenient way of deflecting the responsibility, but it's not necessarily any less evil.
I don't take the personal experience and interpretation of a single person to be much evidence for the existence of this vaguely defined concept called willpower, but just thought this anecdote would be of interest
I think there is some effortful thing in the mind that sometimes needs to be engaged to accomplish something, but perhaps that effort is expended at a different level. Maybe it's constantly bringing a goal to mind, to support one decision making process. Maybe it's breaking a habit by avoiding what triggers it, or creating a new habit. Generally, expending conscious effort to change the tracks of the unconscious train, not by steering it.
It's too facile to call it willpower though; I think it needs to be more strategic than that, and I think the baggage of the word is unhelpful.
"Willpower" isn't usually used to refer to ways to plan the context of your decision outside of the "very hard", tempted-to-give-in timescale, so that the temptation to give in is lessened (i.e. the decision is no longer "very hard.")
Of course, you're still correct in a sense: it requires willpower to even take the steps to work on your life to fix problems. This is the point of prescribing antidepressants to depressed people: usually the drugs themselves aren't enough to fix someone's life, but they give them the boost they need to start fixing their life (by attending therapy sessions, getting out of bad relationships/jobs, etc.)
What ever it is called, we face decisions in life. Do I get up with the alarm to go to work and earn a living or do I stay in bed (continually) and get fired? What's for breakfast? What to wear? Which way to travel? ....... Now, a lot of these decisions are pretty easy to make but that changes day to day. It largely comes down to this: When we have the mental energy and aren't stressed, we tend to think through our decisions, weighing pros and cons. When we are stressed or upset or depleted, we tend to react and just choose something and ignore consequences. Saying "just remove the stress" is just as hard and unreasonable as "just choose to stop drinking".
Anyone who is interested in this subject should also read Thinking: Fast and Slow. It goes fairly deep into the kinds of studies and implications of choice referenced in this article.
The point here is that the thing which decides whether or not someone succeeds at changing themselves is not the having/not having of willpower, it's everything else. And willpower as a concept is just one more distraction.