If every car were custom made, you'd have no idea which control had what function... look at how differently a mass produced car used to work before things were standardized https://www.hagerty.com/media/car-profiles/driving-a-model-t...

You can't fix something you don't understand, and unique things require a lot of time to figure out.

This applies in many areas. I learned a ton about Atomic Clocks the first time I fixed one... the second time I did it, it was only an afternoon, instead of a week spent in my friend's shop over the course of a month.

So, yes... the main investment is the knowledge learned. It is foolish to waste that effort.