Some ideas behave like slow weather. They gather quietly, almost invisibly, in the background of ordinary life. You hear them now, and then, you sense them in passing, and you notice them taking shape in conversations that do not yet sound like conclusions. Then, one day, the sky seems to change all at once. A phrase is suddenly everywhere. A new habit feels normal overnight. A once-unthinkable opinion becomes mainstream. A slight movement becomes a crowd.

The shift can feel so abrupt that it is tempting to believe something mysterious happened, something beyond the usual logic of human behaviour. People often describe it as if a switch had been flicked: yesterday, nobody thought it; today, everyone does. Yesterday, nobody did it; today, everyone is doing it.

This sense of sudden collective change is the emotional home of the "hundred monkeys" story, one of the most repeated modern parables about social tipping points. The tale is usually told with confident simplicity. A group of monkeys learns a new behaviour, washing sweet potatoes in the sea to remove sand. The habit spreads slowly among the group. And then, at a certain threshold—often dramatised as the moment the hundredth monkey learns it—the behaviour leaps across boundaries. It appears on other islands, among monkeys that supposedly had no contact with the original group. A new idea has reached "critical mass," and now it seems the whole world receives it.