I went “under the knife” two weeks ago to repair a severed tendon in my left shoulder. The surgeon did some amazing work, judging by the photos I’ve seen, and he hopes I will regain a fair amount of strength in that arm.

Of course, with the surgeon’s work completed, mine began. I have a twice-daily regimen of exercises for the next 12 weeks, with periodic appointments to assess my progress. It’s easy for the surgeon to determine how diligently I’ve followed his instructions: He pulls and pushes against that hand to see how well I resist, then he watches while I dangle the arm loosely and let it swing like a clock’s pendulum. If it swings freely, he knows that the shoulder joint remains flexible. If not, it proves that I have not done my exercises–increasing the danger that my shoulder will stiffen and “freeze.” That would be the worst possible outcome.

That shoulder is a good metaphor for much of my life as I grow older. To stay flexible (physically, mentally, spiritually), I must use the capabilities I have, even when it’s painful.

Now anyone who knows me well realizes that I’m no paragon of self-discipline. I avoid pain as much as possible. But if I refuse to move, think, and stretch myself spiritually, there’s a real danger that I’ll stiffen in place.

Someone has said that the worst malady for an aging person is “hardening of the categories,” the unwillingness (and, eventually, the inability) to look at life in fresh ways with an open, pliable mind. So I keep on volunteering for activities I haven’t done before, reading books by unfamiliar authors, and striking up conversations with perfect strangers.

Does that feel uncomfortable and even irritating at times? Of course. But it’s the price of staying flexible.