I consider the loss of certainty a sign of wisdom. I was full of certainty when I was 17; 20 years later, I'm full of doubt. And I'm pretty sure I know more now than I did back then.
It seems like people can follow two paths as they age. One path is to develop ever-greater certainty about the world--this is the stereotype we often see about inflexible senior citizens, clinging to the world of their youth.
My friend Don (who is 77) often tells me about how many of his contemporaries now spend all of their time watching Fox News. They seek out media that confirms their existing views--this isn't unique to the aged, but seems particularly pronounced in the case of Don's friends.
The other is to realize that the world is full of uncertainty and ambiguity, and to take a more forgiving approach to all aspects of life.
It's up to you which path to choose as you grow older.
(This post originally appeared as a comment on my friend Lindsey's blog)