If someone falls into the breach, they help someone else out - by taking a stand on their behalf or by taking on their behalf. But what exactly is a breach?
This is how the holes shot out of fortress walls during trench warfare have been called since 1600. The soldiers who defended these holes from the fortress and tried to close them were of course in great danger. If one of them fell, another soldier had to immediately step up and step into the breach for him.
