Any number of things can trip one up if they haven't been identified, so aren't being proactively managed. It could be as simple as "I have allergies and I don't know it, so I can't connect the dots that when I do X, I am exposed to something I am mildly allergic to and then I accomplish a whole fat lot of nothing."

The problem, of course, is that I find the majority of things I do fall into that latter camp where I can't muster the drive to put in effort.

Please just start reading the resources I pointed you to.

There's also this, which I am the author of, though there isn't much there currently: https://raisingfutureadults.blogspot.com/