Here's my definition of maturity. Yours may vary, and I'm mature enough to realize that, and perhaps even appreciate it. But here's mine: If you find out you've been wrong about something, and you respond by changing your mind, and feeling grateful for having learned something, then you've shown the cardinal sign of maturity. If, instead, you get really angry, and insist that you "are too right!" then you've shown the cardinal sign of immaturity.
In other words, maturity is when you have an ego, immaturity is when your ego has you.
Here's why I think it's important. The number one problem facing our civilization today is our collective lack of maturity.
A classic example: The Iraq War was a terrible mistake, but those who questioned or criticized it have not gained stature or influence because of their superior good judgment in not going along with a very bad foreign policy blunder. Instead, they've been treated like they should apologize for getting it right. (And even then, the apology should probably not be accepted.) Who is listened to instead? Who is on cable TV, writing on the op-ed pages, taking up space on the Sunday talk shows? Those who got it wrong. The hook-line-and-sinker crowd. But it's not just the media, it's the Obama Administration as well. Who is running America's foreign and military policy? Again: Those who got it wrong.
How about torture? The outing of Valerie Plame? Any of the Bush national security screwups? Any of them? FISA?