If you roll a die (one dice), a “one” might appear by chance, but if you continue to increase the number of times the die is rolled, the ratio of times that “one” appears will approach one time out of six. As in this case, when the number of trials is increased, the law of large numbers indicates that the results will approach a fixed value. When calculating the probability of accident occurrence, the probability can be forecast by analyzing large volumes of accident data rather than just looking at the accident percentages of a few cases.