Few mistakes are as dangerous or as costly. If you make a minor mistake as a surgeon, the patient may die – sure. If you make a minor mistake as an astronaut, you may die, your crew may die, and millions of dollars may go to waste. Something as simple as making sure a tool is secured tightly, a container is fully closed, or a surface is wiped dry could mean the difference between life and death.
Ice cream scooper. All it takes is one peanut allergy.
There are many where you absolutely shouldn’t make a mistake, but in most cases, as long as it really is a mistake you still can make it and your life will be more or less fine on the other side.
I guess personal doctor to a warlord or third world dictator might be different.