This article pretty much sums up why I keep starting new projects instead of finishing things. The bigger a project becomes, the larger the model, and the longer it takes to mentally restore that model each time you start working on it, thus decreasing the number of opportunities you get to actually work on it.

The code I generally author certainly isn’t easy to write. I spend considerably more time thinking than I do typing. The mental model I need for comprehending code when I read it is static. My working model for writing code is highly dynamic.