Mark Cuban shares a strict rule about his time

A serial entrepreneur, Mark Cuban, moved from billionaire to famous person when he joined Shark Tank as a guest in 2011, then as a full-time panelist the following year.

On the show, he invested in over 200 companies, but not all of those deals worked out well.

"By Cuban's own estimation, roughly one in four of his 'Shark Tank' deals "have done really well or crushed it," he told a local ABC News affiliate. "Fifty percent ... have been good and continue to go on, and 25% where I just think to myself: 'What the hell was I thinking?'"

His "Shark Tank" investments, however, have made him money.

"Cuban invested 'about $33 million' in total during his time on the show. From those investments, he estimates he's received up to $35 million in cash returns, and his mark-to-market equity from those businesses is worth "at least $250 million," he told CNBC Make It.

Investing in so many companies gives Cuban dozens, perhaps even hundreds of partners vying for his time. In a recent Instagram post, he shared how he handles that.

Mark Cuban has one clear rule

Cuban, who still owns a stake in the Dallas Mavericks but no longer controls the team, wants it known that not every "Shark Tank" investment was about making money.

"I don't do the show to get the best investments," he wrote on Twitter in July 2022, in a post that no longer appears on the social media platform, now known as X. "And I don't always invest because I think I'll make money. Sometimes my deals are purely to help [an entrepreneur] or send a message."

Making an investment does mean committing time to your new partners. Cuban also has a rule for how he manages all those relationships.

In the Master Class post on Instagram, the serial entrepreneur explains how he responds to requests from partners or associates asking for a "quick call."

"I'm like, no, I don't do calls, you know, I'll engage with you via email, and trust me. I do this all the time. I'm really good at it. I'll give you more comprehensive responses than if it was via phone," he shared.

Using email allows Cuban to step back and be thoughtful.

"And, if we do it by phone, I'm gonna forget half the stuff that we talked about because I've got so much going on. If we do it via email, I can search for it always," he added.

Experts don't always agree with Cuban

While Mark Cuban has rigid views on not taking calls, communication experts say the effectiveness of email versus phone calls often depends on the situation.

Stanford Graduate School of Business lecturer Matt Abrahams has said communicators should first ask, "Is this the best channel for this message?"

Even though Cuban's approach works for him, phone calls do come with a lot of positives.

Multiple communication experts say calls work better for urgency, emotion, nuance, and relationship building, while email works better for documentation, clarity, and non-urgent communication

Phone calls can also make people feel valued.

"Whether they're your coworker, client, investor, teammate, or employee, people want to feel that you value them and respect their time," according to the Quo Blog's Kenza Moller, who suggested phone calls in certain situations.

• When you're covering something complicated
• When the matter is urgent
• If strong feelings are involved

The last one could be the one that saves the most time and keeps the relationship on track.

"Strong feelings like distress or anger can damage a business relationship if handled poorly, so if negative emotions may be at play, it's best to make a phone call to avoid assumptions and misinterpretations," Moller wrote.

Warren Buffet does not use email.

"I'm not big on time management. I just see what I need to do and I do it. I don't use a computer. I don't use email. I just don't have that much time for that sort of thing," he told CNBC.

Cuban's pro-email stance isn't new. He actually commented on not taking phone calls or meetings back in 2016.

"No meetings or phone calls unless I'm picking up a check. Everything is email," Cuban said, in an interview with Arianna Huffington's media company, Thrive Global.

From his perspective, email is a productivity tool.

"Love it. Live on it. Saves me hours and hours every day. No meetings. No phone calls. All because of email. I set my schedule," said Cuban.

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This story was originally published May 21, 2026 at 7:07 AM.