Why are so many people so mentally limited by their assumptions?

Question:

Why are so many people so mentally limited by their assumptions?

Can they not see what is actually there?

Additional Details

19 hours ago
That's exactly what I mean. Already most answers assume I think I'm not included in this, but I've never said that at all.

Best Answer - Chosen by Asker: 19 hours ago
That's exactly what I mean. Already most answers assume I think I'm not included in this, but I've never said that at all.