I own 115 games on Steam. I went through the list to see how many I actually finished. And by finished I mean totally finished. The result:
Seven.
And that's just Steam. I never finished any Final Fantasy after IX, never finished Dragon Force, and most embarrassingly, I have an original copy of Panzer Dragoon Saga. Yes, that game that goes for $300+ at auction. Got about halfway through and got tired of it.
It's funny. It seems like the more games you have, the less inclined you are to stick to any one of them. I have at least played all of them, even if only for a few minutes.