Things tend to look better from a distance than they do up close. This also applies to how we evaluate our past actions. The distance, in terms of time, tends to cause us to look more favorably on ourselves.
Each of us have done some truly hurtful and foolish things in our past, but we usually see them as less damaging than they actually were. Even when we acknowledge this truth about ourselves, it can still be difficult to see the effects of our past actions in an accurate way.
But acknowledging this about ourselves, is a step in the right direction. It can at least make us less arrogant and think more carefully about the potential effects of our future actions.