For example, I know many devs (myself included) that work professionally on big and successful projects as part of a team. We often work on projects in our spare time but they tend to get dropped within a few weeks and never really go anywhere.
It feels a lot more like a battle of willpower than one of skill in these situations. With the willpower to stick to a project and work on it for even two hours a day for a full year, I have no doubt it'd end up as something to be proud of.
At some point, I read a blog post about how we have a finite amount of willpower per day, and focusing on a task costs a large chunk of it. However, once you do something regularly enough it becomes a habit/routine, and the willpower cost decreases making things easier. I'd like to believe that's true, though have not committed hard enough to my own work to know if that's really the case.