It's true in the real world too which is why even in secure buildings a person can often slip in by coat-tailing someone. Stopping every single person to check ID is cumbersome and slows everyone down. People have stuff to do.
Truly high security environments are zero-tolerance, which makes them annoying and expensive to work in. I've talked to people who have worked in US military and CIA/NSA places and a very meaningful amount of time is spent complying with security and jumping through hoops. Even with all that, stuff gets leaked and stolen.