I was reading the Wikipedia page for The Magicians, doubtless one of the most reliable sources of information on the internet, and ran into a section naming the characters informing the reader of "Margo Hanson, equivalent to Janet from the novels. Her name was changed to avoid confusion with other names beginning with 'J'".
I've seen this several times before in renaming the characters of movies and television series derived from books, and I'm curious why it's so common. Sure, you want your characters to have distinctive names, but why is it so necessary that no two characters have names starting with the same letter?
It seems that the amount of upset one would earn from the fans of the original book by changing the name of a beloved character would more than compensate for the tiny number of viewers who would grow confused and stop watching if two characters had names with the same first letter.