Walt Disney was told a mouse would never work.

Before Walt Disney built the empire he has today, he was fired by a newspaper editor because "he lacked imagination and had no good ideas."

In 1921, Walt formed his first animation company in Kansas City, where he made a deal with a distribution company in New York, in which he would ship them his cartoons and get paid six months down the road. He was forced to dissolve his company and at one point could not pay his rent and reportedly survived by eating dog food.

Also, When Walt first tried to get MGM studios to distribute Mickey Mouse in 1927, he was told that the idea would never work because a giant mouse on the screen would terrify women.

Entrepreneur Walt had a whole slew of bad ideas before coming up with good ones, read about them here.