Anesthesia
Since the beginning of time, only minor painkillers like opium have been available to patients undergoing surgery; these drugs have little effect on more serious surgeries like amputations. Over 170 years ago, the development of anesthetic caused this to shift, along with the healthcare industry. It's inconceivable to the majority of us that this hasn't always been the case.
Although though anesthesia is unquestionably amazing, we still don't fully comprehend how it affects the brain. Despite the fact that anesthesia is a particularly enigmatic component of the equation, it has to deal with the more general subject of how consciousness functions, which we'd come to in a moment.
For starters, we don't know why it just affects the brain and not other body parts. Patients under anesthesia appear to be cognizant and pain-free while still having their other capabilities, such as cognitive ability, active and functioning as they would when awake. We simply don't know what region of the brain it alters or whether it affects everyone in the same way, which is likely why anesthesiologists are by far the most well compensated medical specialists practically everywhere in the world.