In many cases of real experiments, the set of possible outcomes is not known and neither is the number of favourable outcomes for the occurrence of a particular event. This is why it is necessary to conduct the greatest possible number of attempts.
For example, imagine that a company has asked its customers and friends to drop their business cards into a box for a draw to win a cruise for two people. When the draw is made, we don’t know how many cards were dropped into the box or where they come from. If we are interested in the probability of randomly drawing the business card of a woman who works as a florist, it is clear that we do not have any information to determine this number. However, by making several draws from the box, we will get closer and closer to the real probability, and only after we have completely emptied the box of all possible outcomes will we have the exact answer.