I spent over $400 on a certain free-to-play stronghold-building game, over a few weeks, after intending to spend only about $5 or so testing it.

It was very interesting to introspect on the self-rationalization, etc, all the while understanding that I was BS'ing myself and also understanding the tricks they were using. It was addiction, pure and simple.

Now, part of the reason I didn't stop sooner was that I can afford that, although it's not a good use of my funds. That was actually built into the rationalizations: Oh, if I'd taken the car to work today I'd have spent $20 on parking, and $15 on lunch, so I'll just take the subway and bring my lunch tomorrow ...