Key is that this person didn’t even know he was infected the second time. As I understand it, we are constantly subject to reinfection by other corona viruses. But they don’t take hold (I.e., don’t replicate) to any degree the second time because of your immune system’s learned response and you are thus not infectious.

Or you can take the pessimistic view that this virus is somehow different. We have no lasting immunity even after being exposed. Which blows the rationale for lockdowns right out of the water. If you take the pessimistic view, you’ll just have to come to grips with the fact that this will be with us for the long term and it’s another risk we’ll have to learn to manage.