Okay kiddo, so you know how some people want to do good things in the world, like police officers who want to catch bad guys and save people? Well, sometimes those people start to think that their good cause is so important that they can break the rules to achieve it.
For example, let's say a police officer wants to catch a really dangerous criminal who has hurt a lot of people. They might start to think that it's okay to break the law themselves in order to catch the bad guy. This is called "noble cause corruption," because they're doing it for a good cause (catching the criminal) but they're still breaking the rules (by, say, using an illegal method to get information).
The problem with noble cause corruption is that once someone starts bending the rules a little bit, it's easy for them to keep going further and further until they're doing really bad things without even realizing it. And even if they do realize it, it can be hard to stop because they've convinced themselves that they're doing it for a good reason.
So while it's important to want to do good things in the world, it's also really important to follow the rules and not do bad things, even if we think it's for a good cause.