There is the concept of "Defense in depth", used by the military for many years... This acknowledges that each layer is bound to have holes, therefore the best

There is the concept of "Defense in depth", used by the military for many years... This acknowledges that each layer is bound to have holes, therefore the best you can hope for is to delay the inevitable breach. Therefore, any additional layer you can add to the security increases the time taken and hence gives you a better chance at rebutting the attack.