I cannot tell you how many meetings I've had where someone told me I "wasn't communicating clearly" and I asked them to read the unclear message back to me so I could understand what would make it clearer for them.
And then I find out they can't read, at least not fluently. They either skip key words altogether or mistake them for other words.
I'm convinced fewer than half of American adults could read a random book out loud, fluidly, without preparation.