Okay kiddo, sometimes when people write articles or do research, they want to make sure that everything they said is true and accurate. This is where peer review comes in. Peer review means that other experts in the same field of study take a look at what was written and make sure everything makes sense and is correct.
But sometimes, even with peer review, mistakes can happen. Sometimes the people doing the peer review don't catch a mistake or don't look closely enough at some important parts. This can lead to bad information being published and spread around to other people.
Sometimes, people can also be dishonest and purposely put false information or lies in their writing. If the peer reviewer doesn't catch it, then it can become a big problem when people start to believe these lies or false information.
When peer review fails, it can have consequences. People may start to lose trust in the information being published, and it can be hard to know what is true and what is not. That's why it's important to keep working on making peer review better and catching any mistakes or false information.