I would say, not letting go when I disagreed with some decision I knew was wrong. Younger me would tend to tenaciously fight those, to my detrement. You end up

I would say, not letting go when I disagreed with some decision I knew was wrong. Younger me would tend to tenaciously fight those, to my detrement. You end up getting a reputation for being argumentative or hard to work with. Later I learned waiting things out and more subtle ways to affect change.