I don't think about my life in terms of a career <...> Or, more precisely, I can think and talk about best career moves etc. all right, but this thinking and talking doesn't affect my real decisionmaking. This is driven by the need to find meaning in life and the urge to use life as an opportunity to make a (positive) lasting impact. If I were doing software for [whatever], I would feel that I'm wasting my time and my life on trivial pursuits. This feeling would make me totally unable to continue, or indeed even to start, doing software for [whatever].
... I am generally satisfied with my math books and papers. I always have doubts about my ability to come up with any new results of the quality comparable to my previous work, though. That's what worries me. Now that the most important of my 10-15 year old ideas have been written up, I may well be heading for another midlife crisis. But we will see.