I wonder if instead, kids simply learn it as their brains mature. That is, maybe the repetition does nothing but annoy everyone. There are all sorts of studies that show that brains continue to mature even into the twenties. When, as a kid, I heard the phrase "Think before you act", it was usually not in the context of major life decisions -- it was in the context of measure-twice-cut-once situations. To be fair, some of these could turn out to be major life decisions (i.e. diving head-first into an insufficiently deep pool), but they aren't intended to be so.