I like Harvard materials but they do tend to the abstract and the verbose. Which makes the following article even better as it is short, sharp and extremely practical.

http://blogs.hbr.org/schwartz/2011/11/four-destructive-myths-most-co.html

The myth of the benefits of multi-tasking is very prevalent. But it should be obvious to anybody who has done it that the constant switching of tasks is very inefficient. You lose your train of thought, you need to get back up to speed and you need to spend time organising yourself.

In many cases, it is better just to get your head down and get on with a task until it is finished.

Many of us fear finishing tasks because that is when we get judged. So we have many projects at a nearly-finished stage. It takes just a moment’s thought to see that that is wrong.