https://www.amazon.com/Tiny-Habits-Changes-Change-Everything...
So I think Piers is skating over that very important part of the equation.
Another piece of it is, if you manage to get healthy somehow, sleep better etc, then your motivation changes; the base level is reset. You have more energy to spare which you can devote to goals.
But I think there is a simpler way to think about motivation, which comes down to the ratio of effort to reward. The smaller the effort-reward ratio of a given activity, the more likely one is to do it. That single idea seems to rule my own behavior and that of many people I see. But it's also something you can hack, partly by using Fogg's idea of starting small. To change a behavior (and ultimately, your life), you just need to find a small enough starting activity to trigger action. It's not about motivation at all, and all the "motivational speakers" out there are misleading people in some fundamental way about the path to change.
One of the traps in that dynamic is that as we decrease the magnitude of the activity (drink a glass of water as oppposed to "go to the gym once a week to get stacked"), our motivation decreases as it loses its grandiose visions of change. I don't think task size and motivation necessarily decrease at the same rate tho. And I do think that grandiose visions are sometimes a form of self-sabotage or psychological homeostasis; ie "i'm only motivated to do things that i can't follow through on."
The degree to which impulsiveness can be directly reduced is an interesting question. I think a big part of the human condition is a frustration with one's impulsivity, and I suspect that that's driving the surge in adult ADHD diagnoses in some countries.
Which comes from "The Procrastination Equation" by Piers Steel, an academic focused on motivation. I haven't finished the book since it's pretty self help-y, but I do like the equation. Here, expectancy is perceived likelihood of finishing the task, value is obvious, delay is how long until the payoff, and importantly, impulsiveness is the general impulsiveness of the task doer.