Too many times you put the diagram down in front of them and watch their eyes glaze over, regardless of how critical or how simple it is.
"Just take care of it." stops being a statement of delegation and changes in meaning to; "This is beyond me. I don't want to deal with it. Don't bring it up to me anymore."
Yeah, I have lost count of how many times a new manager has come in, found out that I’ve been with the company for like 2 decades and nobody here knows how to do the things I do, and they say “he needs to crosstrain people, etc”. And then after the first attempt that that, they stop talking about it, and then a month or two later I get a raise without asking for it :)