Do celebrities really die in three? Actor Malcom-Jamal Warner, singer Ozzy Osbourne and professional wrestler Hulk Hogan died in late July, prompting Google search around the “rule of three” to spike.

Ever walked into a grocery store for milk and walked out with a cart full of stuff you didn't plan to buy? You're not alone. The thing is, most of us don't even realize we're being influenced. We ...