When you think you’re pretty well-off — and then you send your kids to private school, and see that you’re actually among the poorest families there.
(Not quite our family, as it happens, and not that it’s anything to be ashamed of; indeed, the school-poor families are probably the ones who are sacrificing the most for their children’s educations. But I’ve noticed people talking about this before, both from their own perspective and from the perspective they imagine their children taking, and it strikes me as an interesting phenomenon.)