When worldbuilding, always consider how your system could be exploited in ways that wouldn't be obvious to you.

One of the most important things I've discovered in my several decades of worldbuilding is something that I can only call "strategic thinking". When making a new world rule or system, you can't just consider the good impacts and the negative impacts, you have to consider the ways in which a savvy and intelligent individual or group could exploit that system. If you don't do that, you'll end up with a system that is wide open to problems. For example, I was building a fantasy world with a pantheon of gods, and I decided to have an afterlife system where the soul is judged based on good and evil deeds. The final result is a somewhat Christian afterlife system, except the neutral souls go to a neutral realm.<br><br>The problem with that is that it presents a paradox - if the neutral realm is better than the Hellish one, then wouldn't a somewhat evil person be better off just being a little evil? The good afterlife is closed to them, so why not just take the middle path that is somewhat evil? The only way to avoid that is to have the neutral realm be somewhat worse than the Heavenly one. However, if that's the case, why would someone who's already going to be in the neutral realm want to be good at all? If they're already damned to a somewhat Hellish place, why not commit the odd evil act or two and enjoy life? This presents a problem, as the world's justice system is based on the idea that if you do enough evil acts you're damned for eternity, which isn't much of a deterrent based on the system I described.<br><br>This kind of thing happens everywhere in worldbuilding. If you think you've created a foolproof magic system, someone will almost always find a way to exploit it in a way you didn't expect. That's not a bad thing, as long as you're willing to adapt and change your system based on the information. Eventually, you get a system that is watertight, or at least as much as it can be.<br><br>This applies to every act of worldbuilding. From how a justice system operates to how magic works. From how a government functions to what the laws of physics are in your world. The most important thing is to think carefully about how a system could be exploited.