Think of it like high school. Level 1 is like being a freshman. Everyone has roughly the same basic elementary knowledge. Some might be better at some things than others, but they are still babies in even those areas, unless they're prodigies.
Level 4 is like maybe Junior. You have, by this point, started to really veer towards one path or another, but you still need a lot of refinement.
Then Level 5 is like you are on your last year of high school. Now you are really choosing your major and charging towards your career. After that, you are like in college until maybe level 8. Now you are a true pro, and you are significantly better at your craft than everyone else.
But that's not how D&D portrays experience levels, is it?
Level 1 characters are already young professionals with training even though inexperienced. A proper comparison would be graduates. In 5e a level 1 bus driver with no medical training can succeed in surgery where a trained surgeon can lose a patient. We even have an actual scene for that on the nautiloid. =)
Ah, but that's not a skill proficiency issue. That's a difficulty issue. See. Brain surgery should be more like DC 20 or 25. It should be near impossible for an untrained character to pull off. Only a level 8 or 10 character with single or double proficiency should have a chance of success in such a task. The reason we have characters with no proficiency being able to do things that only a professional can do is because the DC is not high enough to illustrate that only a professional can do it.
So, taking the nautiloid scene, if a bus driver can still succeed in performing the brain surgery task of removing the brain, what Larian as the DM is saying is that this particular brain surgery is something anyone COULD do, whether an expert or not. If you are a young medical student who has some proficiency in surgery, you might have a better chance of success than Mr. Bus Driver, but you still lack the training and experience to gain a significant advantage over Mr. Bus Driver.
That is the misunderstanding many have with D&D. Just because I create a cleric with Medical proficiency, it doesn't mean Im a young professional at it. It means I have some very basic knowledge of it and interest in it. That gives me and advantage in that area over someone who has no real interest or training in it it all. As I gain levels, NOW Im becoming a young professional.
And the idea is that just because Mr. Bus Driver doesn't have any proficiency, it doesn't mean he has NO knowledge in that area. It just means it is not his strong subject. When you succeed in a dice roll where you are not proficient, it is like the character saying, "Wait! I actually know this. I learned it from this or that past experience."
So maybe Mr. Bus Driver succeeds in removing the brain because somewhere in his past he sat in a surgeon's office and was bored and studied the guy's brain surgery poster diagram showing how to do it.
