Heathrow Harry,
True, but it enables you to deploy your limited resources in the most efficient way (of vital importance in the anti-U boat campaign).
I believe that, right to the end, Hitler and the German Intelligence believed that the Enigma system was inherently impregnable (and really, if you examine it closely, most people would agree).
It was the special genius of Turing and all who worked at Bletchley Park that achieved the seemingly impossible. It is arguable that he saved Britain.
D.