Choose a huge mistake you've made, and turn it into advice for a kid to understand. Be creative lol... Listen kid, There are these chemicals in your brain called serotonin and dopamine; they make stuff fun, and that's all you need to remember and know for now. The time will come where you are faced with a decision of making everything you enjoy now double the fun. This is when you remember serotonin and dopamine! Doubling your fun costs serotonin and dopamine, and you only have so much of them. If you get greedy it will be all gone and you won't have fun again for a very long time.