The way I think about it is, if I randomly pick a sample from the sampling distribution, what's the 99% chance, or how many, let me think of it this way, how many standard deviations away from the mean do we have to be that we can be 99% confident that any sample from the sampling distribution will be in that interval? Another way to think about it, think about how many standard deviations we need to be away from the mean. We're going to be a certain number of standard deviations away from the mean, such that any sample, any mean that we sample from here, any sample from this distribution has a 99% chance of being with plus or minus that many standard deviations. It might be from there to there. That's what we want. We want a 99% chance that if we pick a sample from the sampling distribution of the sample mean, it will be within this many standard deviations of the actual mean. To figure that out, let's look at an actual z-table.