The IKEA effect is not "self assembly", the IKEA effect is "I think of this piece of furniture more highly because I assembled it myself". The IKEA effect compares how people feel about the same piece of furniture when they've assembled it themselves vs when someone else did it.
You may love it because you made it, fine. But you also may love it because it’s exactly what you need. You may hate it because you tried to build it on a shoestring budget and you got what you paid for.
What’s similar to IKEA, as in the self-assembly bit, but also doesn’t have the “it’s exactly what I need” effect that confounds the “I love it because I assembled it myself” measurement?
Or maybe I’ll just call it the Effort Effect. Ugly, but I’m not much of a marketer so I’ll take it.
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...
And maybe this study should be taken with a grain of salt too.