I read something recently by Arnold Schwarzenegger that said that when it came to fitness and overall health, in his experience and observation "motivation always fails" and that it's ultimately first and most about building "habit and routine".

So to speak to what you said, "I want to work out so I lose the weight" eventually breaks down, but "I'm doing a quick light workout after my morning (nighttime) coffee because that's what I do to get energized, and when I get off work in the morning I'm going to go for a walk before bed - because that's what I do" - that's sustainable habit and lifestyle and for me it's almost always worked, and it tracks with both your both and what Arnold said.