Years ago I was working on developing a new cloud native service. The particular microservice I was working on had to call out to multiple other services, depending on the user parameters. Java 8 had just come out and I implemented what I thought was an elegant way to spin up threads to make those downstream requests and then combine the results using these fancy new Java 8 stream APIs.
I realized at some point that there was a case where the user would want none of those downstream features, in which case my implementation would spin up a thread that would immediately exit because there was nothing to do. I spent a couple days trying to maintain (what I saw as) the elegance of the implementation while also trying to optimize this case to make it not create threads for no reason.
After a couple days I realized that I was spending my time to try to make the system sometimes do nothing. When I phrased it that way to myself, I had no problem moving on to more pressing issues - the implementation stayed as is because it worked and was easy to read/understand/maintain.
To this day, I avoid the trap of "sometimes make the system do nothing". One day, that performance optimization will be necessary, but that day has not yet arrived in the ~7 years since then.
We were behind schedule and had, I think, three separately implemented/maintained/deployed services that needed to be able to access the internet to do their work. Rather than implementing the intended auth mechanism in each service, writing tests for it, going through code review, and redeploying, I instead added nginx to the base Docker image they all used, configured them to send requests to that nginx instead of as normal, and made that nginx instance man-in-the-middle our own services to attach a hardcoded HTTP header with the right creds.
I man-in-the-middled my own services as a hack - dumb but it worked. It was meant as a quick hack but stayed for I think a couple years. It did end up being eventually being the source of an outage that took a week to diagnose, but that's a different story.