Answer: Bertie knows Gussie well, especially that Gussie tends to get into trouble.
In "Extricating Young Gussie," it is clear that Bertie and Gussie know each other very well. This is likely to be the reason why Aunt Agatha asks Bertie to stop his cousin Gussie from marrying a vaudeville performer. She is concerned that Gussie will make a mistake by bringing such a woman into his aristocratic family. It is clear from their dialogue that Gussie tends to get into trouble, and that this is something that Bertie know.
