The key principle behind GTD is writing down everything that you need to remember, and filing it effectively. This seemingly simple point is based around far more than a simple filing cabinet and a to-do list. Allen’s system is like a to-do list in the same way a kitten is like a Bengal Tiger.

“Filing effectively”, in Allen’s sense, means a system with three parts: an archive, where you store stuff you might need one day (and can forget until then), a current task list in which everything is stored as an action, and a “tickler file” of 43 folders in which you organise reminders of things to do (43 folders because that’s one for the next thirty-one days plus the next 12 months).

The current task list is a special kind of to-do list because all the tasks are defined by the next action you need to take to progress them. This simple idea is remarkably effective in helping resolving the kind of inertia that stops us resolving items on our lists. As an example, try picking a stubborn item from your own to-do list and redefining it until it becomes something that actually involves moving one of your limbs. Something necessary but unexciting like “Organise a new fence for the garden” becomes “ring Marcus and ask who fixed his fence”. Or, even better with further specifics on how to move your fingers, “dial 2 626 81 19 and ask Marcus who fixed his fence”.