That is not correct either. Who considers finishing an IKEA build an achievement?
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.
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.