da Vinci was famous for getting merrily lost into rabbit holes and missing deadlines. He gets a commission for a painting, and slowly starts mixing paints for weeks. Then he has an epiphany about an interesting paint mix, and gets lost into mixing paints for weeks on end. He ends up not delivering on his commitment.
Another example: he spent a lot of time dissecting human corpses and horses and made many draft drawings. Then he declares in his notebook something like, "I'm going to write a treatise on human anatomy; it will be better than those created by surgeons because I can draw exploded views of arms and muscles from different angles." He never finishes it. But, he discovered[2] the functioning of the aortic valve in the heart!
In his notebooks[1], you'll also see his frustrated attempts at learning Latin, and many other fascinating examples.
Definitely read Walter Isaacson's bio of da Vinci; it's riveting.
[1] http://www.bl.uk/manuscripts/Viewer.aspx?ref=arundel_ms_263_...