I have to admit; I get tunnel vision a lot. Way more often than I'd like. Ok, I'm getting ahead of myself here.
See, in some scenarios tunnel vision is incredibly good. It lets me finish things quickly and solidly. Many times I've had 'moments of clarity', where I was able to blaze through the idea -> creation -> verification -> shipping in a matter of minutes. And do it considerably well.
Unfortunately, tunnel vision has been kicking in way too often. In conversations, relationships, creations, and simple moments of life, like doing errands, commuting, working, etc. This whole 'focusing on one thing only' thing gets frustrating after some time. Sometimes, I get so focused on one imaginary outcome, a manufactured goal, that I can't see anything else. In conversations, I can't hear people not talking about the things I'm focusing on. When thinking, for God's sake, I can't think of anything not related to 'the thing'.
I'm still struggling with how to combat this. One approach, although pretty obvious, has worked quite often so far; distraction. Simply distracting your mind from the thing you can't stop thinking about might work. The bigger & more surprising, the better.
I also find simple walks pretty calming. While oftentimes I go on 'think-walks', where I deliberately process through a particular thought or idea, sometimes, in the right circumstances, I can turn this around and think about everything and nothing. Some big picture stuff, but mostly stillness. And appreciation.
All in all, tunnel vision is quite good. I can't imagine how people do stuff without it. Yet, as with everything in life, it has another side to it.
And, because of that, it can be balanced.