Why did Leonardo da Vinci finish so few paintings?

Leonardo finished few paintings because he worked like a researcher, not a production line. He studied anatomy, optics, water and machines, filled some 13,000 pages of notes, and treated each picture as an experiment. That made his paintings revolutionary, but slow, often abandoned, and sometimes physically fragile. Fewer than 25 major works are attributed to him, and many of them are unfinished.

The pattern shows up early. Of three important works he took on in the 1480s, two were never finished, and the third, the Virgin of the Rocks, dragged on so long that the client only got it in the next century. In Milan, a writer watched him paint The Last Supper from dawn to dusk without eating, then not touch it for three or four days.

His experiments could backfire. Instead of reliable fresco, he painted The Last Supper in tempera over a dry ground, so he could work slowly and revise. The surface grew mould and flaked, and within a hundred years a visitor called it 'completely ruined'. His later Battle of Anghiari mural also decayed and survives only through a copy by Rubens.

Late in life, a record says his right hand was paralysed, which may be why the Mona Lisa itself stayed unfinished. According to the biographer Vasari, a dying Leonardo regretted not practising his art as he should have.