I've adopted a policy of only buying if I am playing it instantly.
I don't care if it's on sale or not, if I'm not playing it in the next hour I'm not buying it.
I've never had a backlog since then, and never bought any games I've never played.
Most of the time, the biggest hurdle to a backlog is playing the first 10% of the game. Once I do, the other 90% comes much easier.