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For knowledge workers, there is a lot of work to do defining our work before we can start actually doing our work. The 5 phases of workflow is the GTD model for capturing, defining and doing our work.
The practice of regularly and completely emptying all of your inboxes so that your trusted system is updated with the outcome of processing all of the new stuff. The opposite is trying to use, for example, your email inbox as a management system in itself.