“Adversity doesn’t build character, it reveals it.”

Has been attributed to both:

1. Vincent Thomas “Vince” Lombardi (1913 to 1970) was an American football player, coach, and executive in the National Football League.
2. James Lane Allen (1849 to 1925) was an American novelist and short story writer whose work, including the novel A Kentucky Cardinal, often depicted the culture and dialects of his native Kentucky.

I also found this (Debate.org, 2012):

“Terms:
Character: The mental and moral qualities distinctive to an individual.
Adversity: Difficulties; misfortune.

Some believe adversity builds character. I disagree, and believe that adversity reveals character. Adversity can bring out the worst qualities in you or the best qualities in you. Either way, it reveals your character.

Adversity is thrown upon us [not necessarily, think Special Forces training] and we must react to it. It reveals what is existent in us. Though character can change, it takes time and an accumulation of experiences and how we think about them and apply them to the type of people we are and want to be. A single circumstance of adversity can not build character.

Watch your thoughts, for they become words.
Watch your words, for they become actions.
Watch your actions, for they become habits.
Watch your habits, for they become character.
Watch your character, for it becomes your destiny.”

Reference

N.D. (2012) Adversity Doesn’t Build Character; It Reveals It. Available from World Wide Web: http://www.debate.org/debates/Adversity-doesnt-build-character-it-reveals-it./1/. [Accessed: 05 September, 2016].