It's easy to say "document what you can" when you leave "document", "what", and "can" loosely undefined. The article gives us a why and then leaves out the who, what, when, where and how.

If you observe people in their daily work, you will see there are many reasons why people do not document things. Time constraints, incentive structures, liability, general trade-offs and ambiguities. This is true not just in software/engineering but in any line of professional work.

There's plenty of grandstanding about the importance of documentation, but not much interest in understanding why people don't document in the first place.