system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are illnesses like chickenpox normally harmless in children but deadly for adults?

Just curious since you would think that the more robust immune system of an adult would make the illness less dangerous.
gpt
Generally kids have weaker immune systems than adults do. Symptoms of disease are sometimes products of the immune system fighting the infection. Since adults have stronger defenses against infectious diseases, adults will have worse and more apparent symptoms.