Because if we could, we’d fuck it up immediately.
Pain is important. You generally need to know if you’re hurt, and pain is a pretty clear way for the body to communicate that. If you could turn it off, everyone would have it off all the time, and people would die from the most treatable injuries/illnesses just because the body’s natural alarm system didn’t function.
Imagine you could alter your heart rate. The internet would be filled with sketchy forums with “how to overclock your heart and maximise your potential” type posts, which would probably cause heart failure pretty soon in anyone who tried it.
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