It was two nights before Christmas when a 17-year-old invited three friends to his house to hang out. The friends arrived. The teen showed his friends his new pistol.

Imagine you’ve scrimped and saved money to one day build your dream home. You selected the location and the construction company to work with—a brand new home to your specifications is within your grasp. Until it isn’t.

When you are a law-abiding, kind, person it’s hard to understand someone who seems to have been born evil, heartless, selfish, and...