So if you took a sample right over here, and you calculated its sample mean, and you happen to fall in this area, or this area, or this area right over here, then you would reject your null hypothesis. Now, if the null hypothesis actually was true, you would be committing a type one error without knowing about it. But for power, we are concerned with a type two error. So in this one, it's a conditional probability that our null hypothesis is false. And so let's construct another sampling distribution in the case where our null hypothesis is false. So let me just continue this line right over here, and I'll do that. So let's imagine a world where our null hypothesis is false, and it's actually the case that our mean is mu two.