Companies spend millions of dollars on firewalls, encryption, and secure access devices and it's money wasted because none of these measures address the weakest link in the security chain: the people who use, administer, operate and account for computer systems that contain protected information.
A company can spend hundreds of thousands of dollars on firewalls, intrusion detection systems and encryption and other security technologies, but if an attacker can call one trusted person within the company, and that person complies, and if the attacker gets in, then all that money spent on technology is essentially wasted.
I use Mac. Not because it's more secure than everything else - because it is actually less secure than Windows - but I use it because it is still under the radar. People who write malicious code want the greatest return on their investment, so they target Windows systems. I still work with Windows in virtual machines.
People are prone to taking mental shortcuts. They may know that they shouldn't give out certain information, but the fear of not being nice, the fear of appearing ignorant, the fear of a perceived authority figure - all these are triggers, which can be used by a social engineer to convince a person to override established security procedures.