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Magic??
Some people are quoting that graph as if every infection follows that graph perfectly. Each infection is unique.
An infection may last a very short period if the body's defences act on it quickly (you're immune system can only deal with the virus when it is in your body, immunity isn't some magic forcefield that prevents you being infected). An infection may also last a lot longer than the graph suggests, even asymptomatically.
That's all.
Magic??