How to teach a healthy dose of skepticism?

c0d3h4x0r writes: "It's no accident that "whatcouldpossiblygowrong" is one of the most common tags applied by Slashdotters to stories about proposed ideas or laws; the ability to spot and predict faults is a big part of what makes a great engineer. It starts with having a healthy skepticism about the world, which leads to actual critical thinking. Many books and courses teach critical thinking skills, but what is the best way to encourage and teach someone to maintain a healthy dose of skepticism? Is it even teachable, or is it just an innate part of the geek personality?"