Here is one of my favourite clips from Seinfeld which shows how a monopoly is broken.
The Soup Nazi makes delicious soup—so good there’s always a line outside his shop. He refuses service to Elaine, and by a stroke of luck she comes across his stash of soup recipes. She visits his shop and informs him that his soup monopoly is broken, while waving his recipes in his face. Also in this clip, George gets charged $2 for a roll that everyone else gets for free. This example of price discrimination shows that in order to charge different customers different prices, you must have market power. Source: Seinfeld Economics