The date was July 5, 1991, and Bill Gates was a 34-year-old billionaire already, running one of the most successful and important companies in the world--yet a venture that was known from the outside as the "Evil Empire."

Gates was a very busy person. But it turns out his parents were having lunch with someone else they wanted him to meet: Warren Buffett.

"It was a funny event because my mom's very sociable, always getting people together," Gates told a group of students during a joint appearance with Buffett. "I, at this time, didn't believe in vacations, was totally focused on my job. So when she said to me, 'You've got to come out and meet Warren...,' I said, 'Mom, I'm busy!'"

By the way, July 5, 1991 was a Friday, which means a great many Americans were enjoying a four-day summer weekend. But Gates was planning to work until he was cajoled into making the trip out for lunch.

As history records, it was the start of a beautiful friendship, if you ask either Gates or Buffett. The two men talked for hours that day, and struck up a friendship that seems to run deep and true, and to have been rewarding for them both. 

More than that for the world, however, since it was the spark of a philanthropic bent in Gates that ultimately led to the Giving Pledge and multi-billion-dollar charity efforts by the Bill and Melinda Gates Foundation.

I also think it was crucial for Gates, because it provided him with something he might not have even known that he needed, and that would have been almost impossible to find otherwise: not just a close friend in Buffett, but a mentor.

I say this not because Gates wasn't already successful. He was, and far beyond what most people will ever have the chance to achieve. He was worth more money and had a bigger impact on the world than almost any of his peers. 

Plus, he achieved it all while spurning most of what society tells us to do (for example, dropping out of Harvard).

And let's also add that Gates had only really only ever had one job in his entire life: leading and building the gargantuan company that he founded, from a tiny little startup to one of the juggernauts of his industry.

But you know what? It turns out that wasn't enough.

That's why I've written recently about the key decisions Gates made 20 years ago--thus, nine years after he first met Buffett--that meant he's become the rare person to have truly important second act.

In fact, I'm willing to bet that 100 years from now, people will remember Gates much more for his philanthropy than they will for anything he did as a computer pioneer or an entrepreneur and business leader.

Anyway, think back to 1991. If you're Bill Gates, where on earth do you find a mentor? Do you even let yourself believe you might need one?

So, hats off to the late Mary Maxwell Gates then, for making the introduction, and perhaps even recognizing that her son needed someone like that in his life. 

Postscript: Can you name the other Harvard-dropout-turned-entrepreneur who, much like Gates, has only ever had one job (CEO of the company he founded) and who today wields as much money and power as Gates ever did? 

Not only that, but he's almost exactly the same age that Gates was when he met Buffett?

Of course, we're talking about Mark Zuckerberg. 

And apropos of nothing, wouldn't it be awfully smart if Zuckerberg's mom, Karen Kempner, could invite that nice Mr. Gates over for lunch sometime--and maybe convince her son to show up, too?