When we're exposed to a virus do we always become ill?

it all just depends on how high your immune system is, if your high in fiber, protein, and keep yourself healthy, then you can fight off more things, but some illnesses just simply cannot be fought off by your own immune system. take the flu for instance, your immune system is not strong enough to fight it off, but when its over, your immune system will have gained its tolerance, and can then fight that strand of flu off for a while at a later occurance.