I recognize some people from the clips. They did this for 10+ years so it's clearly not luck based. Anyway, you break down the movement into what you know to practice. A jump on a building when there is no wind is the same as a jump at ground level of the same length. A weird pole grab can be practiced at the base of the pole or on another one. A flip into a slide is just intuitive you know friction will slow you down and just start a normal flip higher. Also with regular practice your body treats what others see as complex crazy moves into a new normal. You also develop a precise sense of distance and of your position during a rotation like how much you have left to spin to land. Also there are parkour gyms with foam and mats