I might become a 'finisher'. I have been writing a symbolic math interpretation program for almost a year, and might have it to the point where I can actually run it in the next few months. It's been an idea on paper for 9 years, and I've tried twice before to actually write the software, but got stuck, lost interest and dropped it. I have taken a few breaks from it in the last year, but I keep telling myself, "If you don't finish this, it'll never be more than a crackpot idea on paper, and you'll never know if it's useful." - so I'm doing my best to motivate myself to keep at it. Almost there, and so excited.
I have started and not finished a lot of things outside my field. I was actually thinking this weekend of starting a thread titled, "What do you do with all the ideas you know you're never going to make happen by yourself?" -- because I think of story ideas, inventions, etc. that are out of my field, but which I would love to see happen.
I've tried writing, but I'm just not a writer. Ideas that require some hardware or mechanical engineering are beyond my ability. In the end, I've just decided to focus on ideas in the area I'm most passionate about. Isaac Asimov said something like, "I don't write because I like writing. I write because I can't live without writing." (probably terribly paraphrased and misremembered by me). Since I can stop writing easily, I'm apparently not a writer. But I never stop doing math, so I'm focusing on trying to achieve something new in the math world.