Just a random thought: If you happen to work in an industry, or own a business, where you deal with the general public in any way and someone complains about you, assign that complain zero weight.
One person, out of the thousands that you encounter every week, thought that you didn’t give them 110%… who gives a shit.
The other 999 people that you helped that week were very happy with what you did for them. They just didn’t think it was worth mentioning the excellent service you provided.
That is unfortunate.