A crucial consideration is some fact or argument whose outcome can completely change your approach to a particular problem. If you’re navigating through the wilderness, realizing that your map was upside-down forces you to completely re-orient, and reveals that your entire approach prior to the realization was useless. The same goes for realizing that your compass doesn’t work, or that cell service is available on tall hills, or that the sun is setting and you need to find shelter.
Unless you’ve got every single crucial consideration correct, your efforts will be largely wasted. And unfortunately, the world is extraordinary complicated. The task is set at whatever difficulty Reality chooses, not calibrated to your skill level.
I’ve collected and loosely organized a few considerations I’ve personally encountered, at varying degrees of cruciality.