For most of my life i have struggled with this dilemma. I go into a new project with so much excitement and enthusiasm. But half way through, all of the excitement has worn off.
I have pretty much done all of the figuring out how to do it and worked out all of the details of the design. From there on, it becomes more and more difficult to stick with the project because my mind is already thinking about the next one. It takes a lot of discipline to stay focused on the current project and get it finished properly because, at that point, I have almost completely lost interest in it.
I have theorized that there are two mindsets. A product-oriented person places the highest value on the end result. A process-oriented person is much more fulfilled by the journey and is not nearly as concerned with the destination. I think I am much more process-oriented.
My wife (and a lot of my customers as well) points out that the hardest part of a job for me is the last detail. By the time it gets down to that, I am usually outta there and it seems almost excruciatingly difficult to go back and deal with the just one little thing standing between me and a totally satisfied customer.