Security fails without usability

There's a general trade-off between usability and security. It's an old phenomenon, going back well before the computer age. General Benjamin W. Chidlaw, while commander in chief of the joint service Continental Air Defense Command (part of what eventually became NORAD) in 1954, put it this way:

Simply put, it is possible to have convenience if you want to tolerate insecurity, but if you want security, you must be prepared for inconvenience."

We hadn't yet invented the word "usability" in 1954, but in this context it means pretty much the same thing as convenience. Flash forward to 2014, and it's still the case that if it were convenient to be secure, there wouldn't be so much insecurity about.