A backlog is nearly unavoidable for the average gamer. There's always a game that you are anxiously waiting for and once it is released and acquired, whatever you are currently playing gets tossed on the back burner. This can especially happen around Christmas or birthdays, where you may receive a couple of games at the same time then you either try both, or just play through one entirely before touching the other one. Of course, in the meantime, you may pick up yet another game which stops you from playing the others you received.
For example, last Christmas, I received Demon's Souls, Metal Gear Solid HD collection (which is 3 games), and Goldeneye 007 Reloaded with the PS Move. I had been going between playing Assassin's Creed: Revelations, Uncharted 3 and Batman: Arkham City to try to get all the trophies, but I had at least finished both games so moved onto something new. I really got into Demon's Souls, however I had a newborn son and low and behold Demon's Souls has no pause button. The older my kid got, the more immediate attention he needed, so DS has been put on my back burner as I couldn't guarantee being able to drop the controller at a moment's notice.
I started Metal Gear Solid 2, but trying to go back to older controls after 3 and 4 was hard. I decided to spend my time trying to Platinum Dynasty Warriors 7 (which I did), then went back to Fist of the North Star: Ken's Rage to Platinum it (which I also did). Went back to Metal Gear for a bit, but then it was getting close to my birthday (in July) and I picked up Way of the Samurai 3 since I found it cheap and loved the first one. Played it a bit before my birthday hit and I got Dynasty Warriors Gundam 3 (big fan of DW and Gundam), and Sorcery for the PS Move. Started with Sorcery because I heard it was short, but it being summer the house was often too hot for frantic waving of the Move, so it's on the backburner (and since it is Winter, will probably be played again soon) and went on to DW:G3. I played through that to nearly Platinum (just some multiplayer to do), but picked up Borderlands 2. This being more fun with friends, I haven't finished it since it's hard to get us all together to play. Then Assassin's Creed 3 came out and I am currently working through it.
So in one year my backlog has added Metal Gear HD collection, Demon's Souls, Way of the Samurai 3, Sorcery, Goldeneye, and Borderlands 2. This is on top of wanting to play Metal Gear Solid 4 again since the trophy update, and wanting to go back to finish a bunch of games that I started (Devil May Cry 4, Stranglehold, Folklore, Fallout 3 and NV, Marvel Ultimate Alliance 2, and some others and still wanting to go back to Uncharted 3, Batman AC, Assassin's Creed Revelations). All these games I do want to go back and play, but with having a kid and full time job and spending time with my wife, gaming time can be hard to come by. Plus the holidays are here again so there are some more games in my future. I don't see my backlog shrinking any time soon.