So, you know when you're at a party and everyone starts drinking the same drink? Sometimes, people start saying things like "Drink the kool-aid! It's the best! You'll love it!" Drinking the kool-aid means that you believe what everyone else is saying and doing without really thinking about it for yourself.
This saying comes from a really sad story. A long time ago, there was a man who had a lot of followers - kind of like a boss, but even more important. He told his followers to drink a special drink that he said would make them all go to heaven. But the drink was actually poisoned, and everyone who drank it died.
So when people say "drinking the kool-aid" now, they mean that you shouldn't just do what everyone else is doing without being sure it's the right thing for you. It's important to think for yourself and make your own choices, even if other people are trying to tell you what to do!