Yes, I've noticed two things going on with our familiarity with our kids and theirs with us. When I started homeschooling I thought teaching would be a breeze, honestly. I knew my kids were smart and this K-3 material was SO easy. I didn't realize that what looked basic to me, counting things on a page for instance, was a bit more threatening to them. They could count fine in real life but they needed time to get used to the mechanics of a worksheet or whatever. There IS a step from concrete to semi-abstract.
So sometimes I think I know my kids and what they're capable of better than I really do. There was a rather scary (to me) story on the Pearl website. Their daughter wrote that her toddler kept asking the same questions over and over again. "What's up there in the sky?" She'd get the answer, "Those are stars." and then ask the same question again. The young mother was about to *spank* her for repeating foolish questions -- that's the horrifying part to me-- but then realized that the child was asking the questions *to consolidate and correct her own use of vocabulary and syntax*. Thank God the mother realized this in time, and was able to find ways to cooperate, and did not discipline her small child for a legitimate pursuit of knowledge .
But then there's that other aspect you mention too. The kids know how to push our particular buttons and sometimes take advantage of that. After I pushed one of my kids to frustration by expecting him to do things he was not developmentally ready for, I felt so bad about it that I pulled back way TOO much and the lesson for him was that he could whine and cry when he didn't want to do schoolwork. Obviously that's not the solution either.
I find the best "working" solution to be not to let go of my expectations, but to work differently to put them into effect. I try to communicate to my kids that NOT being able to do something means having to spend MORE time getting up to speed. That's the way it is in the real world. It's not a punishment, just a reality. My delayed child Aidan will be spending proportionately more time on the basics than my advanced daughter who picked up reading and writing seemingly without effort. That way I can let go of my frustration about my kids not performing, and just figure out ways they can learn, and overlearn, the foundational material. It doesn't have to be unpleasant and horrible, but it does have to be done.
But sometimes also as a Mom I have to pay attention to MYSELF as part of the teaching equation and when I'm not functioning at my best, if I'm ill or worried, I put aside what I consider "non-essentials" for the time being. It may not be absolutely ideal, but it lets me keep moving forward.