Studies have found that most people become very set in their ways by age forty or so.  They have finished school, have probably established themselves in a profession, have decided what church they want to belong to, etc.  They have become comfortable to a large extent and don't see any reason to change anything.  The result of this complacency is they stop learning new things, or at least avoid it as much as possible.  Like a pond that is no longer fed by a constantly moving stream, they become stagnant.  After years of this, they are not prepared to make changes when it become necessary, such as with the current economic crisis.  Also, since they stop learning new things, their brain starts to deteriorate, they start getting bored with life and often grumpy about it.  
    All of that can be avoided by following a few simple rules:

• As long as you are alive, and want to stay alive, you need to keep actively learning
• Don't dismiss new things(music, clothing styles, businesses, churches)  automatically just because they are new; take the time to find out about them
• Try to make at least one new friend a year, preferably one who isn't part of your old circle of friends
• Try a new hobby or give an old one you dismissed years ago another chance
• And don't assume your church and your faith has the one and only absolute truth until you take the time to really study the teachings of other churches and faiths.

Following those few simple rules can help us live longer, happier and more productive lives.