To estimate the population using a single point, we can guess that the mean of the sample is identical to the mean of the population (which it rarely is) or can we estimate the amount of error in our sample mean.
Since Sampling Error is almost always present and represents the difference between the data of a sample and the true data of a population, it is often best to estimate the population mean within a range.
Standard Error of the Mean refers to the expected error of a given sample mean. IOW: the extent to which the sample mean can be expected to deviate from the population mean.
