Motivation is key not only to achieve great things, but also to be happy while doing it.
I think a lesson I wish that I had learned earlier is that the order of things are backwards to what I (and afaik most others) had assumed. I always thought that people first get inspired by someone or something, then that motivates them to make a certain effort do achieve those things, and then that has them put in the work to do it. Instead, I've found that simply starting to do something small to bring yourself closer to a desired goal æ, and seeing that it brings you closer, is highly motivating which then again inspires me to do more, which then again makes me do more (creating a positive loop).
Understanding this has made me so much better at taking initiative and getting work done (even if only a little), where before I would have just sat around waiting for something to inspire or motivate me, only for it never to happen.