It wasn't easy to understand the Copernican system in the Galileo's time.
I suppose people didn't understand it because they didn't want to, not because they couldn't manage to. (Same with evolution -- what the OP was about. I might agree about relativity, though I guess for some people at least the absolute denial macro does play some part.)
Galileo was wrong.
More like stuff that was true back them is no longer true now.
I suppose people didn't understand it because they didn't want to
I suppose not. Why? People either have an inborn concept of the absolute up-down direction, either they develop it early in life. Updating to the round (let alone moving and rotating Earth) is not that easy and trivial for a naive mind of a child or for a Medieval man.
A new truth is usually heavy to understand for everybody. Had not been so, the science would progress faster.
Here's the new thread for posting quotes, with the usual rules: