Billionaire investor Thomas Kaplan shares 3 tips for a rich and happy life

Thomas Kaplan is a billionaire investor and "big cat" conservationist.

Matthew Carasella Photography

• Thomas Kaplan says being grateful and playing to your strengths are key to a rich and happy life.
• "Don't be afraid to say, 'I don't know,'" the billionaire investor said in an interview.
• Kaplan sold a Rembrandt for almost $18 million this week to support his "big cat" conservation work.

Gratitude, humility, and conviction are key ingredients for a happy and successful life, Thomas Kaplan says.