Professor Zinkernagel speaks about some historical and more recent aspects of immunology. Although we do know a lot, only about half of what we think we know is usually true - we just don't know which half! Professor Zinkernagel differentiates between scientists who beg for the question and scientists who observe. Scientists can not do better than evolution by using the same tools, only when introducing 'new' tools (antibiotics, antivirals, autoantibodies). Scientists also need to keep in mind that, eventually, the patient is always right. Creative Commons Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales; http://creativecommons.org/licenses/by-nc-sa/2.0/uk/