The rule of thumb in boxing is that after the first time a fighter quits it becomes easier for that fighter to quit in the future. Boxers learn how to give up. After they have dealt with the public chastising once it is easier to do so a second time.
Boxing history is littered with fighters who either learned to quit or learned to stop fighting to win. Oscar de la Hoya was suddenly able to be outworked over the second half of a fight after he decided to retreat against Felix Trinidad. Acelino Freitas learned to quit after his fights against Diego Corrales and Juan Diaz, two men who made careers of out-willing their opponents. The less said about Andrew Golota’s ability to leave a fight the better.
There are numerous other examples.
While this is the general rule, there are fighters who go the opposite direction. There are fighters who so hate the questioning of their heart that they become stronger and re-dedicate themselves to never backing down. Following is a list of notable fighters who quit once and then showed exceptional willpower in subsequent fights.
As a side note: Referencing de la Hoya, Freitas or Golota as having quit a fight is by no means meant to infer that they are in any way cowards. Any individual willing to step into a boxing ring against the likes of Bernard Hopkins, Corrales or Lennox Lewis cannot be deemed a coward.
Also, James "Buster" Douglas is not included in this list. Although he came back from previously quitting to famously upset Mike Tyson, the change in character did not last.