One of the ways I explain my failure (thus far!) to achieve worldwide notoriety is to collect examples of similar underrating of work that, in retrospect, is laughable: (These anecdotes are from memory and thus 85% accurate, guaranteed...)
* The first record label to hear The Beatles turned them down.
* After hearing Hey Jude, the producer (I forget who) told McCartney, "Pop songs aren't that long," to which M replied, "This one is."
* After presenting his findings on the incompleteness of any axiomatic system of arithmetic, Kurt Godel didn't get much reaction. (John von Neumann was in the audience and asked him about it privately, after the talk.) The minutes of the conference didn't even mention Godel's results.
* After showing his results on the existence of an equilibrium in any suitably specified game to von Neumann, John Nash was informed that it was a trivial application of a fixed point theorem.
* George Akerlof's paper on the "market for lemons" was rejected by at least two (I think more) journals before acceptance. Two of the editors told him that they didn't publish articles on such trivialities. (Nash and Akerlof both won the Nobel for these works.)
* Gene Callahan, for the first 8 years of his professional career, was driven to post his analyses of pop culture on a seldom-read web log (or "blog" as it was called in those days) before receiving the prestigious post of C.S. Lewis Chair of Revisionist Science History at Oxford.