The lottery principle involves two different situations, there is a reward and there is no reward. In the case of putting it back, each extraction is an independent event, and the probability of each option being selected remains unchanged. For example, in a random sample of 10 tagged strips, the probability of each strip being selected is110, and the events are independent of each other. In the case of no return, with more gradual progress, the remaining options become less, and the probability of the next round of events will change. This is because you have successfully selected an option from the collection and will not return it.