Events of small probability that have never occurred before may be assessed as having a probability of zero in decisionmaking but this is leads to tragedies in which people find they have been playing Russian roulette without even knowing they are doing so

Could you correct the punctuation please?
Events of small probability that have never occurred before may be assessed as having a probability of zero in decision-making, but this is leads to tragedies in which people find they have been playing Russian roulette without even knowing they are doing so.