As children when we like something, we want more of it. We like playing with a certain toy so the logic goes that more toys will be better. This line of thinking carries through to adulthood.
We get value from one book, so we think having 10 of them will bring us 10 times the same value. We get value from one t-shirt but surely 10 of them will provide more value. A roof over your head is valuable but an extra bedroom, bathroom, double garage, workshop and annex will better…right?