A demanding boss and a high school crush taught Kevin O’Leary one powerful lesson early on in his life.

I recently had the chance to talk with the entrepreneur, chair of O’Leary Funds and investor on ABC’s reality show Shark Tank. “Mr. Wonderful,” as he is dubbed by fans, told me his greatest business lesson came after he got his first job at an ice cream store as a teenager. It just so happened that a girl on whom he had a crush worked nearby.

On his first day as an ice cream scooper, his boss told him to scrape gum off the ground near the front of the store. O’Leary balked — he didn’t want the girl to see him doing that.

When he hesitated, his boss told him, “Listen, you are going to do whatever I say. I am your boss and I hired you to do whatever I want you to do.” O’Leary replied, “‘I’m not going to do that. I’m a professional ice cream scooper.’ And she fired me.”

In that moment, O’Leary decided that he wouldn’t work for anybody else again. Instead of being somebody’s employee, he wanted to be in control of his own destiny. And he has never looked back.

During our talk, O’Leary shared a wealth of advice for entrepreneurs looking to follow in his footsteps. Here are seven noteworthy pieces of advice from the Shark himself: