Truffle ive also wondered when people arrive back in the country...

Truffle ive also wondered when people arrive back in the country from overseas with positive Covid, they spend 14 days in isolation then they let them out, SO what changed in those 14 days, they still come out of quarantine with Covid, it just doesn't disappear, so then they go out in the public again with Covid, they might test negative before leaving but im no doctor or anything so are they saying Covid just goes away by itself if left alone. Obviously im no expert im just struggling to understand why.