[mattkrause]

I guess that's technically correct, in that it's difficult-to-impossible to "know" about someone else's subjective experiences.

On the other hand, painful stimuli tend to (e.g.) increase a person's heart rate and blood pressure, and that the proper anesthetic plane blocks those responses, so it's clearly doing something in the moment. What we don't know every well is the mechanism of action for general anesthetics.