Ashton Kutcher explains his 3 rules of investing

Ashton Kutcher built a fan base as a goofball character in sitcoms and movies, but he has been seriously focused on his investments over the past several years.

It's why his friend Mark Cuban, one of the regular investors on the show "Shark Tank," invited Kutcher to try out for a guest-investor role in the show's seventh season, which began Friday. After getting accustomed to the format, Kutcher dived right in, making a deal, offering entrepreneurs valuable insight, and even sparring with the brashest of the show's investors, Kevin O'Leary.

Rather than begin investing on a whim, Kutcher reached out to prominent Silicon Valley angel investor Ron Conway, who became his mentor in the late aughts.

Since 2010, Kutcher has been an investor through his venture-capital firm A-Grade Investments, which he founded with the entrepreneurs and investors Guy Oseary and Ronald Burke. He was an angel investor before that. He also connected with Marc Andreessen, one of the Valley's premier investors, and Andreessen wisely persuaded him to invest in Skype in 2009.

He has invested in seed and Series-A rounds for companies including Uber, Airbnb, Spotify, and Casper.

In an interview for his website A-Plus, Kutcher said he had three rules of investing, which are focused on what he sees in entrepreneurs:

1. They must intimately understand both their product and their industry.

Great ideas on their own are not sufficient.

2. They must have a personality that will allow them to withstand failure and setbacks.

"You can have the best idea in the world and absolute domain expertise and know how to do everything right, but if you want to do something great in the world, there are going to be obstacles; and you have to be a person who has ingenuity and sheer willpower to get through those times," he said.

3. They must get along well with him.

He's not willing to make a commitment of millions of dollars and years of being an adviser to someone he doesn't want to hang out with.

Kutcher told The Telegraph in 2013 that he was drawn to consumer technologies. "The companies that will ultimately do well are the companies that chase happiness," he said. "If you find a way to help people find love, or health, or friendship, the dollar will chase that."