This does not refer to a lesson in a class, continuing education, school, etc.; but, perhaps some realizations you discovered by living, experiencing things, and how you saw others handle a situation. Maybe it was mistake you made that you wish to never repeat, or conversely, something your did differently this year that you found to be a gem of a way to handle something because of its better results as compared to continuing to do same thing the same way.
So, what was the most important lesson you learned in 2025?