We all recognize the importance of learning from experience, and we all recognize that we cannot reliably remember everything important. So the question becomes - where to store it.
Then the question becomes how to organize it. Do we optimize for quick writes or quickly finding things? Do we optimize for space? Is appearance important? Syncing to mobile devices? Reminders? Right-to-Left writing support? Must the data be in plain text files? Must there be multiple implementations of the technology? Does it run on Linux / Windows / Mac? Does it leak private information? Can I recover it? Does it support embedded images / video / audio / flowcharts / etc.
Etc etc etc