My bike was secured by a well-known maker's lock to the lamppost outside the Town Hall while I went inside for a brief appointment. Somehow, when I took it out of my pocket, the key had broken in half. Next day I asked one of the town council employees cut through the chain for me. At most it took roughly 30 seconds. This was an expensive lock I'd used in several other countries before
Locks are only a deterrent, so the better the lock, the less likely it is a non-pro who has stolen your bike. Whether that brings much comfort, I don't know.