a machine gun nest is a fortified position, you will find nothing like that on a subway;
It was an example I used to prove my point that advancing in the face of mortal danger is difficult. Nobody wants to rush the machinegun nest. As a combat vet you should understand this more than the rest of us. It takes an extremely brave and determined man to do so.
It is exactely the same in civilization. Just plain hard to advance on death.