If by 2009 you had never heard of Pair Programming or TDD, then I would understand if somebody wanted to explain you Polymorphism.

BTW, TDD was not invented as part of XP, it much older than that, probably from the 70s, widely used in SmallTalk and an amazing technique. It helps you refine your objects and method signatures by seeing how they would be used. It helps you think not only the happy path, and so much more.

I have seen examples of a full coding session done through TDD, and I have actually done it several times. You should try it. It actually reduces the amount of errors you make.