Mary, this is superb question, but really you never know things are going to work, that’s why we must all experiment! However, experience does count for a lot. If you watch and listen carefully to others, sometimes you can start to get a hunch for things before they’ve even happened. In my case, lots of other scientists were beginning to wonder and experiment on the powers of the immune system and there were several other experiments that other people published just before I carried out my Nobel-winning work, that made me realise that there must be some way for the immune system could ‘learn’. Big discoveries are almost always the same – taking lots of little bits on information and bringing them together in such a way that shows how the link and why they might be much more important than we’ve realised before.