For me it is just an overwhelming demand that must be fulfilled. Around 20 years ago, before I was diagnosed, I found and went to a store focussed on salt water aquariums. I spent over $1,500 to set up a coral reef aquarium in my living room. I spent another 3 or 4 thousand dollars over the next two years (I wasn't working then and money was tight) and then decided that the upkeep was too much and I gave everything to Goodwill.
I'm damned if I'll be defeated.
Three years ago I got the urge again. While my wife was out of town I spent around $1,000 on a fresh water tank. I kept it less than a year. I knew I didn't really want the thing. I knew how much work it would be. I knew my interest would wane as soon as the newness wore off. But I was compelled and obsessed. I simply could not resist my impulse.
With me it is definitely a "what am I doing?", or better yet, a "Why can't I stop this?"