The actor, in an interview with her 'Wrinkle in Time' co-star Oprah Winfrey, said the decision changed her as a person and more confident, reported E! Online.
"For me, probably leaving an abusive relationship (was the most difficult decision). I drew a line in the sand, and it got crossed, and my brain just switched. I couldn't go any further. I was really young, and it was profound," Witherspoon told Winfrey during last weekend's SuperSoul Sunday programming block.
"I could never be the person I am today. It changed who I was on a cellular level, the fact that I stood up for myself. None of those leaving those situations... it's wrought with self-doubt, particularly if someone damages your self-esteem."
"People say to me that knew me then, 'You're a completely different person'. I didn't have self-esteem. I'm a different person now and it's part of why I can stand up and say, 'yes, I'm ambitious' because someone tried to take that from me before," she said.