Comparative negligence is like when you share the blame for something bad happening. Imagine you and your friend are playing ball and you accidentally break a vase in the room. Your friend may say "It's not my fault, you threw the ball!" But actually, it might be partly your friend's fault too because they were playing along and didn't move away from the vase.
In real life, this happens when people get into accidents or get hurt. The court will look at what each person did that might have caused the accident or the injury. They might say that one person was mostly to blame, but the other person should also take some of the responsibility.
For example, if two cars crash into each other, it might be because one person ran a red light, but the other person was going too fast. In this case, both drivers may be told they are partly to blame, and each person will have to pay for their own damages instead of one person being responsible for everything.
Comparative negligence is like when you and your friend share the blame for the broken vase. It's important to take responsibility for our actions and try to be as safe as possible so accidents don't happen!