Okay kiddo, imagine you have a sandbox and you love building sandcastles. You've built a really big castle and you're happy with it. But then, your friend comes over and starts smashing your castle and building their own right on top of it. This makes it harder for you to keep making your castle bigger and better.
This is kind of like what happens in nature with plants and animals. There's something called a climax community, which is when all the plants and animals in an area have found a balance and are living together happily. But sometimes, something happens that disrupts the balance. Maybe there's a fire that burns everything down or people come in and cut down all the trees.
When this happens, some plants and animals might die or move away. But eventually, new plants and animals start coming in and taking over. They might not be the same kind of plants and animals that were there before, and they might not work together as well. This is called a plagioclimax. It's like your friend's sandcastle taking over your sandbox and not playing nicely with your sandcastle.
So, just like you might have to start building a new sandcastle in a different spot, sometimes nature has to start over from the beginning to create a new climax community.