The names of major characters in a work of fiction need to be distinctive from one another, particularly when the characters are of the same gender. If Susie and Sarah, or Bob and Bill, or Mary Jane and a Maryanne appear in the same stories, readers can become confused. Even somewhat similar names, such as Phoebe and Phaedra, can cause some readers to have to stop and think about which one is which.
Help your readers by ensuring that the first letters of your characters’ first names are different, and if possible also vary the number of syllables in the names of major characters. Use Bob Marquist and Harold Smith rather than Bob Jones and Tom Smith.