It's true, at least partly. I know from personal experience that trying to do too much at once can lead to nothing getting done at all. Then again, there is ev

It's true, at least partly. I know from personal experience that trying to do too much at once can lead to nothing getting done at all. Then again, there is evidence that focusing too hard can be just a strong a cause of brain blocks and burnout. Many famous discoveries were created when the discoverer wasn't thinking about the problem at all. (Eg. Elias Howe and the sewing machine) I think that one needs to find a balance between focus and distraction and between single tasking and multitasking, preferably in favor of focus.