From an interview with Wong Shun Leung:

Q: How did you see the evolution of Bruce Lee from Wing Chun to Jeet Kune Do?

A: First of all, Bruce didn’t get to see the best part of Wing Chun during his early days of training under Yip Man. He then came back to Hong Kong, and truly learned the foundation of what would eventually become his own style. He was a very naughty boy at times but also very smart. So once in the United States, he filled in the blanks in order to make things work for him.

In the later days of his life Bruce said to me, “If I could take back Jeet Kune Do, I’d take it back.” He realized that he could make the movements work, but that was because his style was designed for his own specific talents. His students, however, had problems making the techniques work under real situations. While Jeet Kune Do was a significant art for Bruce, it has not been that way for other people who followed his method.

Bruce was a good fighter, but not as good as movies have portrayed him almost invincible. People used to see Bruce Lee and have Kung-Fu dreams. They wanted to do the same things he did and duplicate his methods. Unfortunately, it seems nobody wants to wake up.