Some reflections by Nick Milton on why knowledge management within organisations is so poor. If I were him, I would have included the below illustration from gapingvoid as I think it illustrates his five points rather well.
Firstly much of the knowledge of the organisation is never codified as information.
Secondly, a common problem (a corollary of the first) is that project knowledge may never have been recorded in project documents.
Thirdly, and a corollary to the first two, the vast majority of project information is not knowledge anyway. If you are relying on project documents as a source of knowledge, you will be relying on a very diluted source – a lot of noise and not much signal.
Fourthly, if there is codified knowledge in the project documents, it tends to be scattered across many documents and many projects.
Finally, many of the knowledge problems are cultural. People are incentivised to rush on to the next job rather than to spend time reflecting on lessons, no matter how important.