The Best Investment the 'Shark Tank' Judges Ever Made f…

Kevin O’Leary, the opinionated and ruthless Shark Tank judge, may jet around the world in gulf streams and throw millions of dollars at risky startups (Toygaroo, anyone?), but he says one of the wisest investments he’s ever made was a stack of Post-It Notes and a pencil.

“I use them at night, before I go to sleep, to write down the three goals I need to get accomplished before I take my first call in the morning,” he tells Entrepreneur.

Related: ‘Shark Tank’ Judges Say Successful Entrepreneurs Share These 5 Traits

While his fellow sharks may disagree with him on many things, they call can proudly list similar products they’ve spent little on that have reaped great rewards in return. 

Bettheny Frankel

“The best thing I ever bought was a cellphone cover with an extra battery. Because my battery dies all the time, and my phone is my business.”

Daymond John

“A pen. Someone wise once said: ‘The dullest pencil will always remember more than the sharpest mind.’ Stop thinking you know it all, stop just listening to things. Especially today where people don’t even write things down because they have these phones. A pen will change your life. I write everything down.”

Rohan Oza

“The car service to go meet 50 Cent to close the Vitaminwater deal.”

That deal, which made 50 Cent the face of the company, ultimately resulted in a $4.1 billion buyout by Coca Cola.

Related: The Biggest Risk 4 Judges on ‘Shark Tank’ Ever Took

Barbara Corcoran

“A copy of How to Win Friends and Influence People by Dale Carnegie. The biggest misnomer in business is that it’s about money, and I don’t know shit about money. I still don’t read a financial sheet, and I haven’t signed a check in my business for almost 25 years. I let other people sign them. I don’t know about money, but what I know a lot about is people. That book puts the finger right on how you develop people talents. I think it’s the best book in the field.”