I think when it comes to "One Thing", I took the view that "Some of us are Bransons, some of us are Zuckerbergs". I always have 6 things on the go, and I don't think I could deal with a life where I only ever focused on one thing.

If you're so inclined, you just need to make sure that you're balanced and disciplined... which is definitely a challenge... but the same probably applies if you're doing one thing :)