"I don't hate her," said Hermione loftily. "I just think she's an absolutely appalling teacher and a real old fraud. But Harry's already missed History of Magic and I don't think he ought to miss anything else today!"
There was too much truth in this to ignore, so half an hour later Harry took his seat in the hot, overperfumed atmosphere of the Divination classroom, feeling angry at everybody.
Harry Potter and the Order of the Phoenix
I'm not sure what the meaning of "There was too much truth in this to ignore" is in this context. Any thoughts?