I like that proverb. I haven't heard it before, but immediately get what it means. And on a related note, I haven't really done mountain biking, but apparently the perfect dirt (called hero dirt) for MTB riding is a day or two after it rains. Neither dusty nor muddy.
Going back and re-reading Ch. 7.3 where we see younger Tozawa-san really drives home just how identical she and Hayato look before she grew her hair out and probably is the contributing factor in Kumasaka's sudden flashback.