Reading comprehension

was one of those things I was, supposedly, taught in school. I usually managed to get full marks for "reading comprehension". It must have been pretty simple I suppose.
There were, at the very beginning, things like "The boy's name was John and he was seven years old" and the question would be, "How old is the boy?" You would dutifully write "Seven" as the answer. It went on. It got more complicated but it was never really that difficult.
Perhaps it should have been more difficult because it seems that many people cannot read with comprehension. Yes, some of this does have to do with the quality of the writing but much more has to do with a failure to actually read at all. People make assumptions about the information which is there. They read what they want to read into something. Sometimes they don't read anything more than a headline - and those of  us who do read beyond that know how misleading those can be. 
Going to university taught me more about reading comprehension - particularly going to law school. My family now has the nasty habit of saying to me - or to Youngest Nephew - "what does this mean?" I don't always know the answer. It is difficult to write clear instructions. I know. I have to write instructions sometimes.
And then there are people who deliberately misinterpret what is written. I know. I should know better. I shouldn't do it. I should be aware that making a comment on a news website is asking for trouble. You can make a plain statement of fact. Someone else will take it as "opinion" and it will lead to a string of remarks about how wrong you are. Try telling people something is not what you said and you will get another string of remarks about how it is what you said. 
I wonder whether those sites should come with a warning?
The Senior Cat tends to write too much. In an effort to make sure he is understood he will write three or four times more words than is necessary. It sometimes makes things less clear.
"What are you trying to say?" I will ask. He sighs and tells me. I dictate the words he needs. Other people will stand there pen and paper or screen to hand and look expectantly at me.
It is not that I am particularly skilled. Part of my job is to make sure the maximum amount of information is given in a minimum number of words or pictures or symbols. Other people could learn to do this too.
They could also learn to read instructions. They could learn to read with comprehension. Perhaps they don't want to do this?