Albert Einstein did not speak until he was 4-years-old and did not read until he was 7. His parents thought he was "sub-normal," and one of his teachers described him as "mentally slow, unsociable, and adrift forever in foolish dreams." He was expelled from school and was refused admittance to the Zurich Polytechnic School. He did eventually learn to speak and read. Even to do a little math.
Louis Pasteur was only a mediocre pupil in undergraduate studies and ranked 15th out of 22 students in chemistry.
Henry Ford failed and went broke five times before he succeeded.
R. H. Macy failed seven times before his store in New York City caught on.
F. W. Woolworth was not allowed to wait on customers when he worked in a dry goods store because, his boss said, "he didn't have enough sense."
When Bell telephone was struggling to get started, its owners offered all their rights to Western Union for $100,000. The offer was disdainfully rejected with the pronouncement, "What use could this company make of an electrical toy."
John Garcia, who eventually was honored for his fundamental psychological discoveries, was once told by a reviewer of his often-rejected manuscripts that one is no more likely to find the phenomenon he discovered than to find bird droppings in a cuckoo clock. (sort of a cute critique actually)
Rocket scientist Robert Goddard found his ideas bitterly rejected by his scientific peers on the grounds that rocket propulsion would not work in the rarefied atmosphere of outer space.
Daniel Boone was once asked by a reporter if he had ever been lost in the wilderness. Boone thought for a moment and replied, "No, but I was once bewildered for about three days."