Have you ever been really convinced you knew how to pronounce a word, and gone around saying it with full confidence in front of friends and strangers, only to find out you sounded like a total nincompoop? That's embarrassing, but what if the entire culture did it all at the same time? Surprisingly, that's how new words are born.
For example, the animal "newt" is supposed to be an "ewt," but people heard "an ewt" as "a newt," and we all just pretended it wasn't a mistake. From "cherry" to "pea" to "umpire" to "nickname" and more, early English speakers didn't seem to be paying very close attention to each other, the French people who conquered them, or the people they conquered abroad. The result are a bunch of words that sound totally normal, until you learn the truth.