One of my undergrad physics professors gave notoriously difficult exams, including an extra-point question that was truly challenging.
A brainiac friend of mine managed to get the extra-point question completely correct. Almost. He screwed up the decimal point, incorrectly putting it two places to the right.
The professor gave him zero points.
My friend was incensed - he did all of the many steps of this very difficult problem correctly, just misplaced the decimal point, and got zero points.
We went to the professor to appeal. The professor's response was: the answer to this question is a temperature. The temperature you got is hotter than the surface of the sun. As a physicist you should've immediately known that's not the right answer. I'm giving you zero points because the point is not to do the steps, the point is to understand the world.