Because here we have, it's a confidence interval for this weird mean of the difference between the sampling mean, it seems kind of confusing, but I just want to restate what we saw in previous videos. This thing right over here, the mean of the difference of the sampling means, we saw two or three videos ago, is the same thing as the mean of the difference of the means of the sampling distributions. And we know that the mean of each of the sampling distributions is actually the same as the mean of the population distributions. So this is the same thing as the mean of population 1 minus the mean of population 2. And this was the neat result about the last video. This isn't just a 95% confidence interval for this parameter right here, it's actually a 95% confidence interval for this parameter right here. And this is the parameter that we really care about.