Fallacy/ˈfæləsi/ Definition 1 of 3Pro Tip 1/3Not Always True Remember, a 'fallacy' often seems believable at first glance but is incorrect. Saying 'It must be true because everyone believes it' is a fallacy. Pro Tip 2/3Beyond Logic 'Fallacy' isn't limited to logical errors, but any incorrect belief. Thinking spiders are insects is a common fallacy. Pro Tip 3/3Evaluate Ideas Use 'fallacy' to encourage questioning commonly held beliefs. It's a fallacy that you can't teach an old dog new tricks.