In life we have to become good statisticians to figure the probability of an event to occur.
You will never know if an event is going to occur with 100% degree of certainty. There is a 99.9999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999% probability that when you put your foot forward to take your next step that it will occur. There is a .0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001% probability that there may be a stroke that will stop your foot from moving forward.
Every event's probability of occurring is different, even for what seems to be an exact event repeating itself. The probability Ranges from infinite 0s followed by a 1% to infinite 9s %. In the middle is 50%. To become a good statistician you must discover all the variables that are involved in an event. Discovering as many of these variables and learning their values is the key to calculating the probability.