ELI5: If the purpose of physical pain is to alert us to injury and help us avoid danger, why is pain sometimes so bad that it incapacitates us?

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To prevent movement that would injure us more, if you break your leg the last thing you should attempt to do is walk on it.

MJMurcott

We get a lot of questions on this theme, like about fever and such, and it boils down to: evolution isn’t an exact science. Evolution basically means, things change at random until one of them is slightly better than the alternative. Human bodies don’t show evidence of having been designed for perfect running. So. We have pain, but sometimes it gets to be too much and does worse than not having pain. We get fevers, but they aren’t as effective as some simple medicines. Basically bodies are good, but understand that our bits aren’t perfect and don’t always do what’s best for us.

Oudeis16

Because our body has limits. Sometimes the injury is so bad that not moving or passing out is the best thing our body can do to protect ourselfs

Lycantree

Doctors always tell you not to ignore pain because it’s your body’s way of telling you that something is wrong UNTIL you get diagnosed with fibromyalgia. Then they tell you that pain is just your nerves malfunctioning, and you should try to ignore it. I’ve been to the optometrist because my eyes hurt. Just fibromyalgia. I’ve been to the dentist because my teeth hurt. Just fibromyalgia. I’ve had x-rays because my hip hurt. Just fibromyalgia. Now I have to practically be dying before I go to a doctor.

purplelikeme

This is the wrong way to think about evolution and biology, kind of. Tissue damage causes certain things to happen, like chemicals to be release and nerves to be active. That is just what happen when you break things. These processes can also do double duty, as any creature that could avoid the thing that makes the process happen would likely survive, so some kinds of warning systems were selected for. As with any physical system, you can overwhelm it, – for example when the damage does not stop, and you cant avoid it by a behavioral choice.

PersephoneIsNotHome