Why do jellyfish need poison?

Jelly fish are an amazing species. They kind of remind me of snakes but like flying. And shaky. They do not all have poison. but some do. If they sting you, you are going to feel it. It wont feel pretty either. Don't let that stop you from being you. I know you wanna be a famous surfer one day and you can be. Just buck up and get out there. Say "Hello jelly fish" and you'll achieve your destiny.