When I started crocheting I developed this interest in exploring all kinds of yarn available. It is difficult to explain, but every time I go to a yarn shop, or a yarn event... I look at yarn and even if I don't need it for anything in particular, if I like it, I buy it. 

Also, when I learn a new technique, I start thinking of all the possibilities. How would this look on a thinner yarn, and on a thicker one, and in this or that colour, and with a thinner/thicker hook? What would be the perfect length? And a new world of possibilities open.

Some ideas never come to fruition or are not good, and hence that particular yarn goes to my personal stash to wait for a new project/idea to come along. Some other ideas require more yarn or less yarn, so I either have to buy more or have some leftovers.