One of the enduring mysteries of human nature is why a very successful business person would give away his time to help an up-and-comer. After all, given the mentor’s success, he easily could charge the protégé $500 an hour for the valuable advice and contacts that he has pulled together during his career.

And yet mentoring is a widely accepted practice. To figure out why, I spoke with Mike Bergelson, CEO of Everwise, a service that connects mentors and protégées. It’s a mentoring company that benefits from being near a key mentor. Bergelson--who started Audium, a software company in New York City that Cisco acquired in 2006--ended up moving to California as a Cisco executive.

He left Cisco and pulled together the team from the software start-up to work on business ideas. But Everwise did not gel until 2012 when Bergelson discussed these ideas with Maynard Webb, his mentor, whose Webb Investment Network (WIN) offers “young entrepreneurs seed capital, mentorship, and on-demand access to experts.”

Thanks to his conversations with Webb, Bergelson decided to focus solely on mentoring. As he explained, “Maynard asked questions that made me realize that I had a passion for creating a way for corporate protégés to find mentors and that addressing that need could be a big opportunity.”

Bergelson knew first-hand how commonly big companies miss the opportunity to match protégés with mentors. That’s because when he was working for one of those big companies, he was given the name of his mentor. That person never responded to Bergelson’s email suggesting a meeting. A few weeks later, the mentor had quit and the company never gave Bergelson another.

Still, Bergelson believes mentoring is a great way for big companies like his former employer to develop talent. A study by a former Sun Microsystems executive found that employees who received mentoring were five times more likely to be promoted. And a study of successful people like Warren Buffett found that the second most important reason they believe they’ve been successful is great mentors (Buffett’s was Benjamin Graham).

Everwise has developed an algorithm that has contributed to a “96 percent match satisfaction rate.” Assuming that’s true, Bergelson should be an authority on why people agree to serve as mentors. Here are his four top reasons.

1. Give Back

Successful people I have interviewed often say that they were helped early in their career by someone who had achieved greatness. Now they believe that they should “pay it forward.”

But why do they feel that way? Some feel that they are repaying a debt to future generations; others believe that if their advice helps a younger person, it will make a little piece of them immortal; still others see mentoring as going back in a time machine and giving a younger version of themselves the advice that they wish they had received.

This last reason highlights the importance of matching the right mentor and protégé. After all, if a mentor finds a young person with similar life experiences--such as emigrating from Chile or competing in triathlons--it will strengthen the feeling of giving back to a younger version of herself.

2. Learn From Process

Many mentors claim that they learn by teaching. This observation brings to mind the Seinfeld episode about mentoring. In case you missed it, George Costanza needs to learn about risk management so he asks his protégé to record herself reading the book to him. (Naturally, Costanza took the idea of learning from mentoring and turning it on its head.)

Bergelson said that many mentors learn through the process of teaching others and they find that mentoring makes them better leaders. He said that 94 percent of mentors agree to repeat their experience because they “take away a lot from the process.”

3. Meet New People

Mentors also like the idea of meeting new people whom they can add to their “I knew when” list. After all, who doesn’t like the idea of bragging to associates that they knew [currently famous person X] before they became successful?

For mentors with this motive, there is also a potential financial benefit. The protégé might offer the mentor an opportunity to invest in an early-stage venture. And if that happens, the mentor may not only get bragging rights but a big slug of cash when he sells stock in the now successful venture.

4. Get Exposed to New Ideas

Protégés also expose mentors to new ideas. For example, the protégé might discuss how her company is using a new approach to innovation, pricing, or customer service. Mentors may be able to apply some of these best practices to their own activities.

People are willing to mentor for free because they already have--in the context of Maslow’s Hierarchy of Needs--met their physiological and safety needs and now seek esteem and self-actualization. Mentoring is a way to get there.