The most vulnerable element of security is human psychology, not the firewall.
Think of a very tall fence and a thick steel door. If the guard opens the door to anyone who says they are a friend, the fence doesn't matter. Similarly, an attacker can call and say they are from IT, asking for the password. The human gives in, not the computer.
Why it matters Today, social engineering attacks are among the most dangerous because they target real people, not machines.