Your advice would be good if there were a way of knowing upfront whether you were in the 80%. Assuming that you are lucky is an extremely poor planning strateg

Your advice would be good if there were a way of knowing upfront whether you were in the 80%. Assuming that you are lucky is an extremely poor planning strategy that, yes, much of the time will result in better outcomes than not. That said, it will also result in some highly negative outcomes in other situations. Insurance has value.