Does anyone have any story of mathematicians who overcame "academic failure" or setbacks to achieve success later as a result of their perseverance? This is a soft question, that hopefully can inspire aspiring students.
New edit: I am especially interested in academic failure (e.g. failure of exams, failure in proof/ wrong proof, failure in getting academic jobs). This is to narrow down the question so it is not too broad. There is another related question on blind/disabled mathematicians which is very good: Who are some blind or otherwise disabled mathematicians who have made important contributions to mathematics?
My ideal accepted answer is a relatively less well known answer (so that we all learn something new), supported by factual evidence (e.g. a hyperlink to a page or a quote).
Some that I can list are:
1) Zhang Yitang, who worked in Subway (arguably a sort of a setback) but later proved a result related to the Twin Prime Conjecture.
2) Robion Kirby, who failed his oral Ph.D. qualifying examination (http://www-groups.dcs.st-and.ac.uk/history/Biographies/Kirby.html) but later proved the "torus trick".
Thanks! (Hope this question is on topic for Math Stackexchange..)