The quote "If your head thinks up mischief, your backside's going to pay for it" from Diana Gabaldon's book, *Outlander*, highlights the idea that one's thoughts and intentions can lead to consequences. It implies that engaging in mischievous or negative thoughts can eventually result in personal repercussions. The phrase suggests a cause-and-effect relationship between one’s mental activities and their eventual outcomes, particularly when those thoughts lead to actions that are less than wise.

This sentiment reflects a broader theme in literature and life where the decisions we make, often driven by our thoughts, can come back to affect us. It serves as a reminder to be mindful of our intentions and the potential fallout from our actions. Gabaldon’s work often weaves in lessons about the complexity of human behavior and the interconnectedness of choices and consequences, encouraging readers to think carefully about their decisions.