It's not so much that I can't remember what happened, but I just stop being motivated to care about what's happening in the game if I take too long of a break. If I stop playing an RPG for more than a few weeks, it's a good bet that I'm not going to finish it. The only exceptions I can remember are FFXII and Suikoden V, both of which I had last stopped for some odd months right outside the final dungeon, and I just had to go through and beat it.