Now that my parents have gotten older, I've noticed that my father is becoming more and more bitter and resentful over how his life turned out, while my mother is becoming more and more at peace with how things have turned out. My father never quite hit his high ambitions, and I can tell that it eats away at him constantly throughout the day. My mother, on the other hand, seems very content with the life she is living.
The study in contrasts is interesting to me, and I think there is something to be learned from both schools of thought. As with most things in life, the optimal path seems to be the middle way. My mother has a very good job and part of that is due to my father encouraging her and pushing her to step outside of her comfort zone and go back to school in her late age. Similarly, my father seems to be (very slowly) mellowing out a little in his late age due to my mother helping him come to terms with how things turned out. Still, there is a lot of bitterness and envy and resentment within him, and it's hard to watch. My mother seems far more well-adjusted now, in comparison.
At the end of the day I think that is what matters most--your relationship to your life. When you strip away all the external things, everything eventually comes down to your thoughts and your mindset and how you think about things. That was the vibe I got from reading this essay, that ultimately things come down to how we reframe things, and that might be the most important "skill" / practice to cultivate.