Motivation is a lie. Drug addicts are motivated. Video gamers. Michael Phelps went 6 years without missing a day of training. You don't need "motivation" when you're already motivated. And if you were the small portion of the population who can actually talk themselves into things, you'd already know it.
People, like every other animal, as mostly a messy bundle of reactions to various inputs. With few exceptions, you can't control this reality. But you can align your short term reactions, the things you actual are motivated to do, with your long term goals, by controlling your environment and the triggers it presents to you.
You can't do the things you should do regardless of the circumstances. But you can make the things you happen to do be the things you should do.