It seems that
'Leonardo rarely completed any of the great projects that he sketched in his notebooks. His groundbreaking research in human anatomy resulted in no publications — at least not in his lifetime. Not only did Leonardo fail to realize his potential as an engineer and a scientist, but he also spent his career hounded by creditors to whom he owed paintings and sculptures for which he had accepted payment but — for some reason — could not deliver, even when his deadline was extended by years. His surviving paintings amount to no more than 20, and five or six, including the "Mona Lisa," were still in his possession when he died. Apparently, he was still tinkering with them.
Nowadays, Leonardo might have been hired by a top research university, but it seems likely that he would have been denied tenure. He had lots of notes but relatively little to put in his portfolio.
Leonardo was the kind of person we have come to call a "genius." But he had trouble focusing for long periods on a single project. After he solved its conceptual problems, Leonardo lost interest until someone forced his hand. Even then, Leonardo often became a perfectionist about details that no one else could see, and the job just didn't get done.'
I had no idea of this, though it rather tallies with the notebooks that were on display at the Chester Beatty Library a year or so ago: page after page of densely detailed notes on hydrostatics with the occasional comment that he needed to be more organised, to manage his time better, to sort his life out.
The article's well worth reading, and makes a serious if counterintuitive case, though its definition of 'genius' is - at best - contentious.