system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How can a sample size of ~1000 people be used to make statistical data about millions of people? Wouldn't the results be way off?
gpt
If you make a pot of soup do you need to taste half of it in order to know the flavor of the entire soup? Of course not, you only need a spoonful to get a general idea of what the rest tastes like. There might be a crunchy carrot or soft potato that don't quite taste the same as the rest but those are not common. 

Statistic principles are the same way but there are certain conditions that need to be met for different tests. Sometimes it's appropriate to use only 30 people while in other cases you do need 1,000 or more people to accurately test the soup.