I tied myself to a ladder in a swimming pool
Why would you tie yourself to a ladder in a swimming pool?
I thought it would be fun to see if someone would jump in to help me.
Pool safety is important and following the rules keeps everyone safe. Horseplay increases the chance of unintentional injury which in itself is bad but can be deadly in the water.
But I wasn't in any danger because I can spend a minute underwater without drowning.
Just because you thought you were safe, doesn't mean that you were. Plus, you could have endangered other people. That's why it's important to always be careful when playing in the pool.