Mass psychology is when a lot of people have the same thoughts or feelings. Imagine if everyone in your class suddenly wanted the same toy. This is a bit like mass psychology because everyone is thinking the same thing. It can be hard to know why everyone thinks the same way, but sometimes it's because people influence each other. If one person really wants the toy, they might tell their friends and then more people want it too.
This kind of thing happens in lots of different situations. For example, lots of people might get excited about a new phone that comes out. They might all want to buy it because they think it's the best phone ever. This is mass psychology because lots of people are thinking the same thing. It's important to remember that just because lots of people feel the same way, it doesn't mean that they are right. Sometimes people can be influenced to do things that aren't good for them just because everyone else is doing it.
So, mass psychology is like when a big group of people think or feel the same thing. It's important to think for yourself and not just follow what everyone else is doing.