what does not destroy us makes us stronger

There is some kind of moral in Robin's most recent entry. Oxygen deprivation at some 5,200 feet above sea level made her sick, then strong, healthy and fit.*
A life that is too easy makes people weak and lazy, inclined to focus on trivial problems. We all need challenges, whether physical or intellectual or emotional (ideally all three) to bring out what's strongest and best in us. We need to suffer a little.
I was very fit when I first moved to Brooklyn, from walking a lot in the cold weather and the general stress and exertion of moving. Physically now I am rather pathetic, but my brain feels like it is working harder than it has in years. I am like a rat put down in a new maze full of exciting-smelling cheese and bright lights. There is so much new stuff to master. Even though it is sometimes overwhelming, I love it. If I could cite one single thing that makes me not regret moving to New York, it is what has happened to my brain.
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*And what about the cooking aspect of life at 5,000 feet? I was always fascinated as a child that the instructions on the cake mix were different for people at high altitudes.