But it isn't.
Neither Hyrum, nor anybody else, has ever seen a system where "all observable behaviors" were depended on by somebody. And if they somehow had, they couldn't know that it hadn't mattered how clear the documentation had been.
There are two much weaker statements which I think are true:
- "No matter how carefully you document your contracts, it will happen from time to time that you leave something unstated and people reasonably guess wrongly what you intended."
- "No matter how carefully you document your contracts, from time to time some people will choose to rely on things you didn't promise, without caring about that."
As well as actually being true, these statements have the advantage of not falsely implying that you can't improve the situation by putting effort into documentation.