People who (voluntarily) undergo a great deal of pain, discomfort, or effort to get something will be happier with that something than if it came to them easily. Ikea uses this to their advantage. Not only does “assemble yourself” furniture save them money and increase their business efficiency, it also has a psychological effect on you as a consumer that gets you to invest in the product.
This is pulled from an interview with Dan Ariely:
The Ikea effect is kind of simple: You build something and you fall in love with it. When marketers do sell you a product, their theory is about preference fit. You like pink and I like orange and I like this a little higher and everyone knows their preference. That’s important. But I think the more important issue is not the preference fit but the investment in the product. Say you like orange and pink. Imagine that in one universe you found shoes that are orange and pink and in other you had to invest five minutes of effort and attention and care to choose the exact shades. What we show is that when you’ve invested into it, you would appreciate them more and you would think about them more. You might talk about them more, you might be more likely to buy them again from the same vendor, your connection would be much higher. It takes very little investment to make something your own. … It’s sometimes surprising how little that is.
Dan Ariely is the best-selling author of The Upside of Irrationality: The Unexpected Benefits of Defying Logic at Work and at Home and Predictably Irrational, Revised and Expanded Edition: The Hidden Forces That Shape Our Decisions.