Over the course of one day, an aspiring entrepreneur asked me to connect her with Richard Branson, an aspiring musician sought to reach Metallica guitarist Kirk Hammett, and a person struggling with depression wanted to talk with Michael Phelps.

Three different people with the same basic goal: Each was seeking--in the entrepreneur's case, "desperately" seeking--a mentor. 

This is something Mark Cuban has never done. (Even though he's clearly more than willing to help others in need.)

According to Cuban:

When I get the opportunity, I'll ask questions. But I can't ever say, ever, where I've said, "I'm going to call this guy and see what he thinks, or this woman." 

Because at some point, I'm going to have to be responsible for whatever that knowledge is. 

I've always had the attitude that there's always something new coming, and whatever it is, it's new to everyone except the people who invented it. I'm at first base like everybody else. Then it's a question of effort. 

In fact, Cuban had a one-word answer when asked if there were ever people in his life he considered mentors: No.

The Problem With Mentors.

When asked, Jeff Bezos's boss at a hedge fund told him not to leave to start Amazon, saying it was, "Probably a better idea for someone who doesn't have a good job."