6 ingredients that go into an apology that has good impact:

1. Expression of regret
2. Explanation of what went wrong
3. Acknowledgment of responsibility
4. Declaration of repentance
5. Offer of repair
6. Request for forgiveness

I wonder what constitutes a declaration of repentance. 

"I won't do it again."

That's a declaration of nonrepeating, which is also important. What counts as repentance?

Pledging change is an essential component of repentance," [1] which literally means to turn, is the activity of reviewing one's actions and feeling contrition or regret for past wrongs.[2]It generally[citation needed] involves a commitment to personal change and the resolve to live a more responsible and humane life."

Ah! The resolve to live a more responsible and humane life! That's it!