One of my favourite comments from a lecturer in my applied science degree: "In theory there's no difference between theory and practice. In practice, there is".

One of my favourite comments from a lecturer in my applied science degree: "In theory there's no difference between theory and practice. In practice, there is". We encountered so many times when theory said one thing but it didn't pan out when tried. It's another way of saying "First, take a spherical cow..."