It is necessary to start forgiving ourselves because mistakes are inevitable and when it happens, we need to let go because carrying the weight forever will keep the wounds open. Self forgiveness actually starts by acknowledging the pain and not passing judgment.
However, it's always better to accept what cannot be changed and learn from it and that's when healing begins. When we release our guilt it brings growth. Forgiveness is a process and letting go one moment at a time will allow us to move forward.