Sometimes students get a little carried away with the "why?" questioning and it leads away from what my course is focusing on which leads me to start discussing something that is covered in one of their other courses they are currently taking. I have to catch myself and stay close to the topic. Sometimes though, it seems the students are put off by the "you'll get to it in your 103 class" type response, and I have to politely explain that we need to stay on topic in order to cover the material for this class. The why on top of why can lead down a long and deep rabbit hole to a point that has little to do with the original topic. This exact thing happens when researching on the internet.