I would imagine Myrna probably has a fairly high opinion of herself. And such praise for his intelligence. This is obviously where he got his outsized ego from.
When he came home from school, beaten up, she obviously placated him by telling him he was better than his aggressors. But he's not.
Also, I wonder if it ever occurred to her that Lucas might have gotten beaten up because of the horrible stuff that comes out of his mouth, not just because he's different and mentally ill.
It's also interesting that she too, just like us farmers in this thread, seems to think that Lucas has dodged a lot of beatings that he deserved. She thinks he's going to end up getting beaten up in an alley. Because she knows the sort of stuff he says, which DESERVES a beating in an alley.
Very interesting stuff from
@Trainwreck