"The locksmith told him that locks are on doors only to keep honest people honest."

"One percent of people will always be honest and never steal. Another 1% will always be dishonest and always try to pick your lock and steal your television; locks won't do much to protect you from the hardened thieves, who can get into your house if they really want to. The purpose of locks, the locksmith said, is to protect you from the 98% of mostly honest people who might be tempted to try your door if it had no lock."

We're only relatively honest. So don't tempt us!

Lots of great material at the link, various studies and so forth. Also this joke:

There's a joke about a man who loses his bike outside his synagogue and goes to his rabbi for advice. "Next week come to services, sit in the front row," the rabbi tells the man, "and when we recite the Ten Commandments, turn around and look at the people behind you. When we get to 'Thou shalt not steal,' see who can't look you in the eyes. That's your guy." After the next service, the rabbi is curious to learn whether his advice panned out. "So, did it work?" he asks the man. "Like a charm," the man answers. "The moment we got to 'Thou shalt not commit adultery,' I remembered where I left my bike."