There's no question that politicians like Donald Trump, Ted Cruz, Hillary Clinton, and Barack Obama are bright, self-assured people. Connections notwithstanding, they would otherwise not have made it to the big stage.
Of course, people are at their best when they embody both of these characteristics. You could be the smartest guy in the world, but if you don't make your points with some level of conviction, no one would ever know it. People won't believe what you're saying -- no matter how ground-breaking or erudite -- if you don't sound sure of yourself.
At the same time, being gregarious won't get you far unless whatever you're discussing has substance. Spouting off nonsense undercuts any confidence you may bring to the table because, after a while, people will simply want you to zip it.
That's why it pays off to become highly knowledgeable in a subject, but also to cultivate social skills. Such an approach will prove invaluable in myriad contexts -- from courting a potential partner to making a presentation at work.
Look around. The most successful people are those who have brains and smarts.
Does this mean intelligence and confidence can't be faked? Absolutely not. But that'll be the subject of a future post.