"No Fine-tuning" - the Condensed Matter Physicists' Version of the Cosmological Principle

Earlier today I was talking to a graduate student about the calculation he is working on. I told him to discard a particular possibility because "it would require fine-tuning". He looked a bit puzzled and asked me to explain what I meant. I actually had to think about that - which goes to show that he was right to ask the question (one often learns most from those one is supposed to teach).