I was thinking that we all learn by experience, but some of us have to go to summer school.

De Vries’s line is a wry twist on the cliché that “experience is the best teacher.” He accepts that people do learn from what happens to them, but adds a comic, slightly cutting qualification: some learners need remedial repetition—“summer school”—before the lesson sticks. The joke works by importing the school calendar into adult life, implying that mistakes recur and that wisdom is unevenly distributed. It also softens judgment with humor: needing “summer school” is embarrassing, but common, and the phrasing suggests a humane tolerance for human slowness and stubbornness.