Multitasking is bad and causes delays

I stumbled upon this interesting piece of information during a project management training. There was a practical exercise to exemplify the problem:

People were split into 2 groups. Group 1 was told to write "Multitasking is bad and causes delays", then number every letter of that text - 1 under M, 2 under U, and so on. Group 2 had the same task, but they were told to write the number under every letter after writing it, so they would write one letter, one number, one letter, and so on.

The result of the exercise was that almost everyone in group 1 was done before the fastest performer from group 2 announced having finished the task.
The exercise was part of a larger session devoted to Eliyahu Goldratt's critical chain project management. His book The Goal introduces theory of constraints, which is a very useful tool for resource planning, and has its applications in both project management and analysis of real-time system performance. The book is a great read, too.