And what do I mean by each flip or each trial being independent? Well, the probability of whether I get heads or tails on each flip are independent of whether I just got heads or tails on some previous flip. So in this case, we are made up of independent trials. So another condition is each trial can be clearly classified as either a success or failure. Or another way of thinking about it, each trial clearly has one of two discrete outcomes. So each trial, and in the example I'm giving, the flip is a trial, can be classified, can be classified as either success or failure. So in the context of this random variable X, we could define heads as a success because that's what we are happening to count up.