When it comes to career advice for the young and unsure, a fierce debate rages. On one side are those who insist that you're most likely to obsess about and therefore excel in fields where you have a natural passion. For that reason, kids should figure out what they love to do, apply themselves, and skills and success will flow naturally from there (though the road may be long, winding, and difficult).

The other camp scoffs at this idea. If everyone thought that way, the world would be filled with (even more) unemployed musicians and wannabe sports stars, they contend. A little realism is their prescription. Find an actual real-world job that's a decent fit for whatever skills you have and that needs doing, and then work hard at it. Like love in an arranged marriage, passion for your work will grow from familiarity, history, and growing competence.

So who's right? A definitive answer is probably impossible, but the first proposition -- that passion leads to skill rather than the other way around -- just found itself another super high-profile backer.

Teenage obsessions make the best careers

Speaking to Harvard students recently, Microsoft co-founder Bill Gates offered quick but simple advice to befuddled young people unsure what career to pursue. In the past, Gates has tried to nudge the undecided toward science, suggesting this would be the area where their efforts could have the biggest impact. But in this latest Q&A, Gates made clear that, at bottom, he firmly believes that the most successful careers are built on passion.

"The thing that you're likely to be world-class at is whatever you obsessed over from age 12 to 18. In my case, it was writing software," CNBC's Kathleen Elkins reports him telling the audience.

Some folks who lacked definite passions in their teens (assuming that passions like my white-hot love of Keanu Reeves at that age don't count) won't find this advice particularly useful. However, if you did find yourself devoting all your nights and weekends to computers or writing or sports in your teens, Gates says you have been gifted a giant clue as to where you're most like to excel as a professional.

That doesn't mean you'll be a billionaire tech founder, national poet laureate, or first-round draft pick, of course. You might end up a freelance programmer, web content specialist (trust me, this is quite possible -- when I wasn't obsessing about Keanu, I spent much of my teenage years writing), or personal trainer. But Gates suggests that if you loved something enough to do it when no one was looking and your devotion paid few dividends, you're much more likely to love it enough to put in the work to become truly excellent in that field.

And that's the best guarantee of success the world can offer.