It comes in two sizes because people are not all one size. There is essentially a man's size and a woman's size. . . but they intermix. My girlfriend's is the 38mm and i have the 42mm. I'm bigger. She's smaller. I have a bigger wrist, she has a smaller wrist. Don't you have any common sense?
They're not just one of two sizes, either.
Don't you have any common sense?
Enough to know that the size is compromise dictated by varying physical attributes of the users, and that "perfect" is an absolute that disallows any possibility of compromise.