Trigger stacking
Stress adding up across a day, so a dog that coped with four things blows up at the fifth — which on its own would have been nothing.
Also called: stacking · why did he snap today · stress accumulation
This is the answer to "he's fine with the postman ninety-nine times and then bit at him". The bite was not about the postman. It was the ninth thing on a day that had already contained a fireworks night, a vet visit, a houseful of guests and a skipped walk.
Stress hormones do not clear in an hour. After a genuinely bad event a dog can sit closer to its threshold for two or three days, which means the same walk that was fine on Monday is a bad idea on Wednesday.
Practically it means a plan has rest days written into it, and it means an owner learns to look at the whole week rather than the incident.