Reading.
Or rather, how so many people seem fear and avoid it, or can't do it. Something like 21% of adults in the US are illiterate, and the majority -- 54% -- read at or below a 6th grade level.
I've been a sight reader probably since I was about six years old. I absolutely cannot look at any words legibly written in my native language and not understand them. You couldn't force me to look at words written in English and not digest them if you held a gun to my head. I fear no wall of text, no matter how tall it is.
It takes some effort to wrap your head around the notion that not only can most people not do this, but statistically speaking most or at least a plurality of people have to struggle or exert conscious effort to read and many of them are loathe to do so. And roughly one in five people simply can't. This did not sink in for me when I was younger.
I can't imagine having to live my life that way. You nerds have seen how much bullshit I write in a day; I'd go absolutely bats.