There’s a fascinating book written in 1921 titled, “Public Opinion,” by Walter Lippmann that answers your question. It reads like it was written yesterday. You can download it for free at: https://www.youtube.com/watch?v=eSVMG_cVFS4
But the short answer is, people look at the same thing but see something entirely different. He gives several examples you’ll instantly understand.
Bkmrk.