If we are open to continually learn, realizing we don't really know as much as we think we do, we have to understand ...... that what we believe now and the way we understand it will change through our experiences. We believe one way, till life teaches us a different view. We can only make our decisions based on what we know already, but that will change and we will then have a new truth.
I believe as we get older, the things that are really important becomes clearer and we realize that a lot of things we thought should matter, really don't. We learn to find ways to be happy where we are, because this moment is all we can be sure of.
Perhaps we also sense our own mortality more and then value the life we have before it runs dry.