I gave up on telling myself that years ago, but I go at a healthy enough pace for it to be alright. The closest I've bought two games together was a span of six months, usually I get one a year. I'm always extremely specific and go for only the game that I want at any given time... but I usually don't want to pay shipping, so in the end I wait for something to pop up within a six hour radius. That's harder than it sounds and sometimes I overpay out of desperation, but I get enough incredible deals the same way that it all evens out. I'm happy with my collection, very satisfied, even, but I always find room for another. I don't see the point of ceasing activity with a hobby, at that point doesn't it become a memory?
Also, I'm a sentimental freak and obsessed with every game I have, so I never sell games to make room or cash for more... that's all done the old fashioned way. That's probably why I'm able to avoid impulse buys, heheh.