To be honest, I know a lot of people don't like Neal Gabler's book on Walt Disney, but I thought it tapped into a lot of the insight he had. I never thought it painted him in a negative light. It painted him as a workaholic, a hard working guy, a perfectionist. I mean, he created Disneyland, you had to have those attributes.
Anyway, Walt himself said that his vision for Disneyland came from sitting on a bench in the park where his daughters would play and dreaming it up. They have that actual bench in Disneyland on display. He said he would sit there while they were on the playground and think of a way that both children AND parents would enjoy themselves.
Prior to that he was a cartoonist, you have to have an imagination for that. He had seen Snow White as a play prior to that. Eventually he started making movies. With the movies came the park, which were inspired by many of his films. Basically he never lost his childlike imagination.