Assume breach

Assume breach means building as though somebody has already got in, instead of only trying to keep them out.

It changes what you spend on. Rather than putting everything into the front door, you add internal doors so trouble in one room cannot spread through the building, alarms so you notice, and a way back that somebody has actually tested. It is not giving up on locks. It is accepting that locks sometimes fail, and that what happens in the next hour is usually the difference between a nuisance and a disaster.