Another anecdote: I finished high school 26 years ago. I too wrote O'Levels and A'Levels. A few things I can share on the classmates I keep in touch with or am aware of what they are up to. The most successful were not the smartest, smart as in top marks in maths which was the gold standard back then. The sentiment you expressed sometimes works in the opposite direction. Because my classmates knew they weren't the smartest, the worked harder in university and in life in general. Hence their success. The smart kids all "made it" but the not so smart kids 26 years later are much better off.