I find that if you can't keep focussed, that's because you are merely excited but not passionate about your work. When the excitement wears off, you crash.
Why do you want to do a startup? What would you do if you didn't need any more money?
A good point. I easily get excited about new ideas and then I start to compromise in the decision to work on the idea that interests me most, or the one that seems the most promising in terms of money making.
I used to want to do research, but these days if I wouldn't need the money, I would probably still do research in terms of doing a startup. I would like to see something useful come off the things I research. I need to do a startup because it is the only way I can see to be able to work on my own ideas and make them real. Not needing money would probably just mean riskier startups.
In theory I could imagine that would be possible within a corporation, too, but I don't see the path for me to get into such a position in a corporation. So the only option I see is to startup.
Why do you want to do a startup? What would you do if you didn't need any more money?