Okay kiddo, imagine you have a bike, and every time you ride the bike it gets easier and easier because your body gets used to it. The same thing happens with some medicines or drugs. When you take a medicine or drug often, your body gets used to it, and it doesn't work as well anymore. This is called drug tolerance.
When you take medicine or drugs for a long time, your body starts to change the way it reacts to it. Your body gets used to having the drug in it, and it doesn't respond the same way anymore. This means you might need to take more medicine or use more of the drug to feel the same effects you felt before.
Think of it like drinking juice. At first, you might only need a little bit to feel refreshed, but over time, your body may need more and more juice to feel the same way. It's the same with drugs or medicine. Your body might need a higher dose to feel the same effect.
This is why it's important to always take the right amount of medicine your doctor tells you to take. If you take more than you should, it can be dangerous, and it can be even harder to treat your illness in the future.