This is oh-so-true, and applies to me quite well -- but I wouldn't, on a whole, say it's a bad thing. While being able to stay "on track" is (of course) very useful, if you do get distracted so easily then perhaps you just need some temporary distance from what you're working on. Or, perhaps, you're working on the wrong thing altogether.

As in my case, I got distracted by a whole new idea while working on one of my other concepts. Was it a good idea to get distracted? Perhaps, perhaps not. Regardless, after some evaluation, I felt as though I needed to take a step away from my other project, and I don't see anything particularly wrong with that.