"After a time, you may find that having is not so pleasing a thing, after all, as wanting. It is not logical, but it is often true." - SpockI have trouble finishing games. It didn't used to be so; I recall renting Final Fantasy 4 when I was a kid and playing from start to finish over the span of a weekend. I finished the original Might & Magic and uncovered the secret of the world of VARN. I completed Ultima 7 and banished the Guardian, then traveled to the Serpent Isle and restored the Chaos Serpent. None of these were short games, but I stuck with them. Now though, I find myself approaching the end of a game and start to get tired of it.
Part of the problem is time. School and homework seemed like so much when I was young, but really I had all the time I needed to game. Nowadays work, social obligations, and family pull me in multiple directions anyway, so it can be hard to fit gaming time in. New games catch my attention and pull me away before old ones are finished. Steam taunts me with games upon games that I've bought and not played for any length of time.
Really though, I think the problem arises when I've reached the point in a game where there's no more real growth to experience but the game isn't over. That point in Skyrim where I've got Dragonbone armor and daedric weapons, and more alchemy items and random gewgaws than I know what to do with. Or in X-Com when I've finished the research and have a fully tricked out squad. The end of the story is still out there, but the things I wanted, I now have. And the having is not so pleasing a thing as the wanting.