Who said "I've learned that success requires mental toughness."?

This quote is attributed to Serena Williams.

I've learned that success requires mental toughness. - Serena Williams

"I've learned that success requires mental toughness."

Serena Williams Strength

Professional Tennis Player American Born 1981 (age 45)

"I really think a champion is defined not by their wins and losses, but by can they keep moving forward after defeat."

"Be bold, be courageous, be your best."

"I really think a champion is defined by their ability to overcome."

"The success of every woman should be the inspiration to another."

"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."