Who said "A man must learn to assert himself or go under."?

This quote is attributed to Jack London.

A man must learn to assert himself or go under. - Jack London

"A man must learn to assert himself or go under."

Jack London Strength

Novelist American 1876–1916

"The proper function of man is to live, not to exist."

"I would rather be ashes than dust."

"You can't wait for inspiration. You have to go after it with a club."

"The wise man doesn't give the right answers, he possesses the right questions."

"Strength comes from within."

"A woman should be proud of who she is."

"A strong woman can overcome anything."

"The only thing I'm good at is killing."