Forgetting is rarely dramatic. It does not arrive as an erasure — a sudden blank where memory used to be. It arrives as a slow shift in what seems worth remembering. The lessons that cost the previous generation dearly become, in the next generation, merely historical footnotes, and in the generation after that, the kind of thing that happened once, long ago, to different people in different circumstances, which is to say: the kind of thing that could not happen now.

This is not stupidity. It is the ordinary operation of a mind that must manage its attention budget. You cannot hold all of history’s warnings in active consideration at once; you would be paralysed. So you let the distant warnings fade to background and attend to the immediate. The problem is that the conditions for repetition are often assembled in the background, in the quiet period when the warning has faded and the crisis has not yet arrived.

The civilisations that have managed best are the ones that institutionalised remembrance — that built into their structures mechanisms for keeping certain hard-won lessons salient even when immediate experience no longer reinforced them. Not as nostalgia or ancestor-worship, but as a functional acknowledgement that the map of past disasters is one of the best guides available to where the new ones might form.

The alternative is to relearn. Relearning is expensive. Its cost is not paid by the generation that forgot but by the one that inherits the consequences of forgetting — which is one reason why each generation tends to believe it has finally escaped the repetitions that afflicted its predecessors, right up until it discovers that it has not.