It is stated in interviews that the reason it was decided that Phoebe would have a twin sister is because Friends and Mad About You aired on the same night, and viewers would be confused seeing Lisa Kudrow in two different shows on the same night. The reason why the Ursula character was not simply dropped was because Lisa, knowing that new shows don't always work out, didn't want to lose a recurring character on an already established show that had a lot of years left on it. The idea of making Ursula and Phoebe twins was then brought up to cover both shows being on the same night.