Dragon Ball Z, Season 8

Goku:
Vegeta, I don't understand. You've never allowed anyone to help you before in your life. Why start now? Why Babidi?

Vegeta:
Because I wanted him to reawaken the evil in my heart. I wanted him to return me to the way I was before! I was the perfect warrior! Cold and ruthless! I lived by my strength alone, uninhibited by foolish emotion! But slowly...over the years...I became one of you, my quest for greatness gradually giving way to this life of mediocrity. I awoke one day to find that I had settled down, formed a family...I had even grown quite fond of them. Would you believe, I almost started to think the Earth was a nice place to live...? Do you understand now, Kakarot? That's why I needed Babidi to set me free. By releasing the evil in my heart, he has freed me of these petty attachments...and I'd have to say, it feels pretty good.

Goku:
Do you really believe what you're saying?