The central theorem of statistics can be thought of like a math equation. It says that when you add up the results of a set of different measurements, (like the height of everyone in a room) the average of those measurements will be close to the same as if you took just one measurement that included all of the people in the room (like the sum of everyone's heights divided by the number of people in the room). In other words, it shows that the average of many measurements will usually be close to the same as the result of one big measurement.