To learn that I love people, and I love the heat and sun.
Before the Camino I was a bit of a misanthrope. Well, not really, but I basically had not only lost faith in humanity, I had never had it to begin with, plus a social anxiety disorder and being an introvert also.
Still an introvert, but witnessing how kind and "real" people were (pilgrims, hospitaleros and locals) was a truly humbling experience and totally has changed my life for the better. Social anxiety is mostly gone by now, and I now love to interact with people (most of the time), even changed my profession towards a more social one.
That and learning to love the heat. No idea how that happened. I had always hated heat and sun, didn't move at all when it was hot, and always stayed in the shade. I remember hot days in Andalucia, back when I was a kid visiting my grandparents, and how miserable I was, sleeping all day, only leaving the appartement to go to the beach, and at night. Now I even like to do extra long walking days on hot summer days, through the afternoon and into the evening. Weird.