Recently, I and several family members and friends were standing outside a locked building waiting for someone who knew the combination to show up and let us in. The door had a five-button lock on it. (I'm not going to identify the building or our purpose for being there so I don't embarrass the building owner or give away the building you're about to learn the combination to.) The buttons were numbered 1 through 5. Talk amongst a couple people who claimed some familiarity with the combination said there were three or four numbers in it. Stephanie spoke up and said she once guessed the combination on the side door to the building. She couldn't remember what it was other than it had 3's and 4's in it.
Years ago, a friend of mine taught me to look at the buttons on cypher locks and check for wear and cleanliness. Unused buttons tend to be dull and dirty. Used buttons tend to be clean and shiny. I took a close look and saw that 1 and 5 appeared to have received less usage than 2, 3, and 4. I stepped back and thought a moment. That selection jibed with Stephanie's story. Since each number can only be used once, it was most likely a three-digit combo. That combination has only six possibilities so if it truly was a three-digit combo it wouldn't to take long to get in. As predictable as humans are, I figured it was not 2-3-4 because those numbers are in sequence. We usually try to mix things up. So after this short period of deliberation, rumination (Bear with me. I'm trying to get back to genius level), and cogitation (How often do you get to use that word?) I stepped up to the door, punched 3-4-2, turned the handle and pulled. To the amazement of everyone--even I was surprised--and to a chorus of "Whoa! How'd you do that?" I opened the door.
So that was pretty cool.