"You can tell every young investor that's never seen a bear market or never used margin ... but until they experience the fear, the darkness and the getting completely wiped down of their account, that's how you learn," said celebrity investor Kevin O'Leary.

There is one investment mistake that celebrity investor Kevin O'Leary will never make again.

"When I was a young Buckaroo trader, I used margins and I got slaughtered. And I never did it again," he said in a recent interview on CNBC's "Squawk Box Asia."