already for a sample of 1000 independent trials, however, the probability that the event "does not" happen in any of them, even once (improbability), is only 0.999 ≈ 0.3677 = 36.77%. then, the probability that the event does happen, at least once, in 1000 trials is or 63.23%. this means that this "unlikely event" has a probability of 63.23% of happening if 1000 independent trials are conducted, or over 99.9% for 10,000 trials.