Whether by accident or research, David Allen tapped into powerful forces in Getting Things Done. There is new research that puts a name to the phenomenon that he discovered. It's called Distributed Cognition, and it is the key to extending your productivity beyond your brain's natural ability.

Distributed cognition is a school of psychology developed in the 1990s by Edwin Hutchins. Using insights from sociology, cognitive science, and the psychology of Vygotsky (cf activity theory) it emphasizes the social aspects of cognition.

This is very similar to delegation within organization. When the load becomes to heavy to bear for the individual, tasks are delegated to others. Like great managers, our minds are able to juggle many different things at one time; however, there is a limit to how many things can be effectively managed at once. That's when we offload things. For managers, that means distributing part of their responsibility to others or buying tools (technology) that helps them extend their own personal productivity.

In the brain, by distributing processing tasks or responsibilities to other people or tools, it is freed up to do more of the strategic things that it needs to do to expand it's influence. This distribution of part of the brain's responsibilities is why the GTD method is so effective. Part of the brain has been freed up to move onto more productive tasks. Here is an article about Distributed Cognition