You make a great point, and it will work for the people who can focus on single tasks. But it’s not something to be prescribed for everyone. Each person works differently, and this self help advice serves to make them feel inadequate or somehow broken if they struggle with focus.

For some it might be better to set up multiple tasks that they can jump between more efficiently, instead of pigeonholing their brain into one place. To the people who struggle with multi tasking, you’re not broken. Focus is great, but it’s not always achievable, instead focus on what works for you. Develop that.