WS MoreOrLess: What is "rare"?

This week: What is ‘rare’? When we say something is rare what do we mean? Lightning strikes which typically kill three people a year in the UK are often described as rare but how do we square that with a condition like motor neurone disease which is also described as rare yet kills 1500 people a year in the UK. Also we speak to Nassim Taleb about his book Anti-fragile.