system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Why does the pain from being stabbed not constantly hurt?

I donate plasma weekly so I get pricked a lot. However within a minute or so after the needle enters my arm I don't feel it there anymore and don't feel any pain until it's removed. Why is that?

Also does that happen with other things? Like being stabbed or having an object pierce your body.
gpt
Pain is a signal from the nerves that run all through your body. These nerves react by sending a signal to the brain when damaged; some react to pressure or temperature, or any of a dozen different stimuli.

That signal doesn't stay at 100% forever however, the signal degrades as the same nerve fires over and over and over; the result is that the pain also tends to be the worst right after the moment of insult/injury.

When you get poked giving plasma, these nerves fire off, then calm down as time passes. When they remove the needle, things move again and nerves re-fire to this new insult; another pain signal.

There are lots of ways this can go awry, and very sharp medical instruments can sever nerves before a signal can reach the brain; and pain in the brain can be adjusted (ie opiates, narcotics, analgesics) but in the body, its all nerves.