It's really not that it's necessarily an achievement, it's a subconscious bias to value the same product higher than if you don't invest time in building it.
It's a kind of "you're rewarded for your effort" idea.
I love building Ikea furniture. It gives me a feeling of completing something that I rarely get building software, where everything is a work in progress. I'm not very good at DIY or craft stuff in general.
I feel way more pride in a Betty Crocker cake than I do about all the Ikea furniture I've built. My Ikea furniture is just cheap but functional furniture. I feel no attachment whatsoever. Anymore than I do taking a toilet paper roll out of the bag and "assembling it into the TP holder"
I feel a sense of accomplishment for few hours after having completed assembly but it's not really much more if any more than the sense of accomplishment I feel when I've finished vacuuming and dusting my apartment.
It's a kind of "you're rewarded for your effort" idea.
I like the cake mix example where letting the consumer add eggs made house wives happier with the cake from https://www.psychologytoday.com/us/blog/the-shaping-us/20191...