Leonardo da Vinci is the original “Renaissance man,” but his interest in, well, nearly everything also came with one big downside — he was a bit of a procrastinator. Compared to his artistic contemporaries, Leonardo didn’t produce nearly as many paintings, with only 20 or so — many of them still uncompleted — still around today. Instead, Leonardo was often distracted, and frequently caught doodling in his now-famous notebooks. Although Leonardo’s life is filled with remarkable accomplishments, it’s also littered with half-realized projects and unfinished masterpieces. One famous example is “The Virgin of the Rocks,” a painting that originally had a seven-month deadline, but took Leonardo 25 years to complete. Other works, such as the Sforza Horse — intended to be one of the world’s largest cast bronze statues — never saw the light of day despite years of work and planning.

His chronic perfectionism didn’t help, and Leonardo himself even lamented his lifelong inattention. According to his biographer and art historian Giorgio Vasari, Leonardo allegedly mentioned around the time of his death in 1519 “that he had offended God and mankind in not having worked at his art as he should have done.” Today, modern diagnoses of Leonardo’s behavior suggest he might have lived with attention deficit and hyperactivity disorder, or ADHD. Modern biographer Walter Isaacson argues that such a diagnosis could partly explain the creative engine behind Leonardo’s eclectic genius.