The human immune system is hormetic, by avoiding contact with mild immune system stressors you are actually weakening your immune system. If your immune system is weakened or compromised, sure, avoid exposure to germs. But if you are healthy you should not avoid exposure to every day germs like cold and flu. It's like exercise, just like your body needs a workout (if your every day life doesn't provide enough physical work) to develop and maintain fitness. Your immune system needs a workout too. Particularly if you live a sterile lifestyle (clean disinfected surfaces, no exposure to dirt or animals). Imagine if your doctor told you. "You're perfectly healthy so I recommend avoiding all physical activity. Otherwise you might injure yourself." This is the immune system equivalent of the masks/ social distancing / lockdowns.