The mood of acceptance or peace is the opposite of Resentment.
Acceptance happens when we can come to terms with we we cannot change. In acceptance, we are at peace with what we consider unchangeable, including the possibilities that are closed as a result.
This does not mean denial of past mistakes or the fact that the actions of others negatively affected us.
We accept the fact that it is not within our power to change the past. This allows concentration on actions which can affect the present and change the future, and avoids being pointlessly distracted with the past.