Unfortunately no one knows what they are. You start with a bag full of luck and an empty bag of experience. The trick is to fill the bag of experience before you empty the bag of luck. If all you can see out of the window is ground that's going round and round and all you can hear is commotion coming from the passenger compartment, things are not at all as they should be. In the ongoing battle between objects made of aluminium going hundreds of miles per hour and the ground going zero miles per hour, the ground has yet to lose.
Good judgement comes from experience.
Unfortunately, the experience usually comes from bad judgement. It's always a good idea to keep the pointy end going forward as much as possible. Keep looking around. There's always something you've missed. Remember, gravity is not just a good idea.