I misspell things on a daily basis. English is pretty bad in this way. I didn't realize how bad English is until I started studying Spanish and Korean. I'd say a lot of Americans don't realize that spelling shouldn't be hard. Most people in the US (75% estimated, no one knows) are monolingual sadly so I'd say a lot of people don't know how bad it is until you explain it to them. But even then, they just shrug. What are they supposed to do about it?
The English classes I remember as a kid didn't ever compare English to anything. It was studying grammar trees and famous books. I think it would have been more interesting if it was like a world religions thing.
Just today I spelled plaguing three ways until I got it right and I'm a native English speaker. Other words I get wrong or have to slow down to type/write: privilege, February, occasionally.
How do I check? How do I find out if I'm right? I just did this today: I googled for "Neil degrasse Tyson" to see if I spelled it correctly. I don't know how to spell his whole name. English first names are pretty common. So I know "neil" and "tyson". Sometimes last names are already other words, like West, Burns, Bush, Love. In that case, you get lucky.
Unknown words aren't very common for native speakers honestly. Reading is the easiest thing. I read Spanish the best and can hardly produce it. Some people would call fancy words "SAT words". SAT is a national test with a vocabulary section in the U.S. (I don't know if this is well-known). It's another way of saying "overly fancy" or "show off" words. Maybe the person is just trying to demonstrate how smart they are or maybe they really do use "SAT words" often. From person to person, it's hard to say. To this point, there are common words and then "fancy words" to some extent. At some level of education, I'd say there are very rarely uncommon words for native English speakers but this is just an anecdote.
If you make up new words, you find that the rules fall apart and English shows it's true confusing nature. I've used this example in the past. Take these two words: tainted and mountain. How do you pronounce this new word: mountainted. Most people I've asked say "moun-tane-ted" even though mountain is "moun-ten".