Warren Buffett knows more about smart investing than most people. But his wisdom extends to other areas of business and life--hiring the right people, making wise career choices, and choosing the right leaders.

But this one takes the cake.  In a conversation with Bill Gates at Columbia University two years ago, which was moderated by journalist Charlie Rose, Buffett shared the biggest decision of his life.

No, it wasn't about some innovative investment choice. Buffett boiled it down to picking the right life partner. Yes, whom you choose to marry makes the biggest difference in your life.

Buffett told his buddy Gates and Charlie Rose:

You want to associate with people who are the kind of person you'd like to be. You'll move in that direction. And the most important person by far in that respect is your spouse. I can't overemphasize how important that is.

This belief has been in motion for a while. The soon-to-be 89-year-old, who is now worth $82.7 billion, was telling his shareholders at a 2009 Berkshire annual meeting the same exact thing:

Marry the right person. I'm serious about that. It will make more difference in your life. It will change your aspirations, all kinds of things.

Research: Marry the right partner and increase your worth

Even research is on the side of Buffett. One study out of Washington University in St. Louis found that having a "conscientious spouse" predicted future job satisfaction and the likelihood of getting promoted. The study, published in Harvard Business Review, also found that marrying up can boost your salary, regardless of gender. How much of a boost exactly?

"With every one-standard-deviation increase in a spouse's conscientiousness, an individual is likely to earn approximately $4,000 more per year," one researcher told HBR

Additionally, "employees with extremely conscientious spouses (two standard deviations above the mean) are 50 percent more likely to get promoted than those with extremely unconscientious spouses (two standard deviations below the mean)."

Another billionaire--Facebook COO Sheryl Sandberg--fully agrees with Buffett's premise of ultimate success. She writes in her bestseller, Lean In, "I truly believe that the single most important career decision that a woman makes is whether she will have a life partner and who that partner is."

Sandberg is talking about a life partner who is fully supportive of his spouse's growing leadership role and ascent up her career path.  

Closer to home, being a conscientious partner in my own marriage, and having married a spouse who returns her conscientious serve, has resulted in both of us being more fulfilled in our own marriage and our work. 

The key was coming to that sharp realization--that a-ha moment--where we both decided we needed to support one another unconditionally to advance the other's career path, rather than competing against one another.

It worked for both of us, and we are in a better and more fulfilling place because of it.