One of the core principles in XP is doing the simplest thing that could possibly work. It’s important to remember that the simplest thing DOES NOT equal the easiest thing.
It’s important to combine the simplest thing that could possible work with continuous design. If you do the simplest thing and don’t also think about the overall design you can quickly end up with a mess.
Does your simplest thing make your design more complex? Does your simplest thing look like a kludge? Is your simplest thing the easiest thing? If so start thinking about what you could do that is simple but NOT easy.
On an XP project it’s easy to say “do the simplest thing”. What isn’t always easy is actually doing the simplest thing. Remember simple != easy.