Not every complaint is negative. Here is an anecdote from years ago.
Optimizing a slow web page was one of the most satisfying assignments I've ever completed. It was a data overview page that took about three minutes to load, which was unsurprising since it performed approximately 2000 queries to gather all the data.
Yes, two, followed by three zeroes.
I was a junior developer early in my career and had never done something like this before. Today, I would probably have started from scratch, but back then, I started chipping away at every N+1 query, multiple DISTINCTs, and away from using non-indexed views (it was a MySQL database).
We went from 2000 queries to 50–60 per request in less than two weeks.
The only feedback came in the form of the funniest complaint I have ever gotten from a customer:
The page is too fast. I used to be able to go and grab a coffee first!
I took it with pride.