I voted 2/3 but the truer answer would be more like 95%. I used to be terrible at finishing games until I made a concious decision to only start a new one after finishing my in-progress title. That's rather sent me too far in the opposite direction - I play games which I'd do better shelving instead of plodding on through. For me to drop a game it has to be physically upsetting (causes problems with my poor eyesight, motion sickness), critically broken in some way, outright repulsive to me, or have absolutely nothing at all which I see potential for enjoyment in. The worst games are the ones which start out ok and then go downhill. It never feels safe to drop them in case they pick back up again.

Sometimes I put a game aside to come back to. I do this when I believe I'd enjoy the game but am not currently in the mood to appreciate it. Also, life happens. I do usually go back to these games.