We didn't pick the echo as our metaphor by accident. It says something about how experience lasts over time.
When a sound echoes, it comes back changed. The walls it bounced off, the distance it covered and the air it passed through all leave their mark on it, so what you hear carries a record of the trip. In that sense an echo holds more than the original sound did. It holds the sound plus everything that happened to it along the way.
Memory works in much the same way. We don't keep experiences like files on a disk, ready to be opened intact whenever we want them. We rebuild them from traces and fill the gaps with guesswork and imagination. Every time we remember something we change it a little, and the memory that comes back has been shaped by everything that has happened to us since.
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