Even when it's something as simple as an IKEA bookshelf, building something with your hands is always a satisfying feeling. According to Psychology Today, it also adds value to an object's worth.
The self-satisfaction of successfully completing a DIY project is really all that matters, but Psychology Today's suggestion is that building things yourself makes you value them higher:
The act of building something, putting your own blood and sweat (and if we're being honest, plenty of frustrated swearing) into a physical object, seems to imbue it with additional value above and beyond its inherent quality, which the researchers dub the "IKEA effect." For instance, in one study, participants who built a simple IKEA storage box themselves were willing to pay much more for the box than a group of participants who merely inspected a fully built box. Participants in another study who constructed their own origami frogs and cranes valued them roughly five times as much as another group of participants thought they were worth. The increased value is not just about effort, but about completion, as built-then-disassembled and incomplete projects received no such benefit.
People like handmade things, and it turns out, they like them even more if they've tried to build something similar. So, is there a downside to all this? Only if you try and sell your custom creations:
So, next time you're debating between that pre-built bookshelf and the the self-assembled one, remember that you'll feel it's more valuable when you put it together yourself. Just don't try selling it.