Simple, perhaps, but a very underappreciated point. All too often I see people make things unnecessary hard for others to do, often consciously, often not. This point ties in with my upcoming article (thanks, NancyLebovitz!) about giving good explanations and passing on your knowledge, since one of the major problems is fighting the urge to keep yourself "irreplaceable".

From that comes the widespread problem of fields being impenetrable and not getting the external review that they need from outsiders.

This (common) insistence, that something takes "years" to understand, is a great example of motivated cognition, as people are deeply invested in others not being able to do what they can, even and especially if that would be trivial to bring about. "It's hard to make a man understand something when his salary depends on his not understanding [how pass on his own understanding]."

Naturally, I'm biased in self-review, but I try to fall on the side of making myself replaceable.

In theory, that will make you "do yourself out of a job", so find a field where the work never ends.