As a rule of thumb for hunter-gatherers walking the African savanna, the Example Rule makes good sense. That’s because the brain culls low-priority memories: If time passes and a memory isn’t used, it is likely to fade. So if you have to think hard to remember that, yes, there was a time when someone got sick after drinking from that pond, chances are it happened quite a while ago and a similar incident hasn’t happened since—making it reasonable to conclude that the water in the pond is safe to drink. But if you instantly recall an example of someone drinking that water and turning green, then
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