How obvious is it really?

I was reading an entry today on another journal about what is so obvious to one person (in this case an agent) is not obvious to another (the writer who she was talking to). It got me thinking about my own struggles with communication, and when I get frustrated by other people. I can be very short after a couple of attempts to explain what I would consider a simple concept. Let me give an example (btw, can you tell I am working as a technical writer right now with all the examples I feel compelled to give).

I work a lot with my mother on her book and the various article that she writes. She loves to email me her articles about a day before the are due needing some guidance. Usually she is upset with her writing and really needs me to just give her a quick edit and mostly (in my opinion) some reassurance that she is not about to embarrass herself in front of her editors. My mother is a great woman, and she deserves a patient editor, but sometimes I cannot deliver that to her, especially when I feel that she is only feeling insecure and not acutally needing my help. So I get snarky, particularly about things that I feel I've already explained to her in previous edits. It is so obvious to me when to use a dash or a semi-colon, but to her (she hasn't worked as an editor therefor is less neurotic about all of this) it is so hard to remember.

I think the longer you are in a profession, the harder it is to remember what is actually common knowledge, or obvious. What about you all?