Leaving notes in a way that takes advantage of our innate relationship with space and context. For example: leaving a post-it note on the door for the next time you head out to remind yourself to buy something you need. This spatial context relationship can be applied to our digital lives as well. Notes that live alongside emails are a much better cue than remembering to check your note-taking app for todos related to the person you are talking to or the email thread.
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Most elements of our digital lives (e.g. apps) only exist within themselves and seldom work together. Because workflows are more useful than point solutions that leaves users with the burden of getting things to work together, humans are the interop layer.