You know the in-flight safety spiel so well that you could probably rattle off the instructions by memory. But have you ever wondered why flight attendants are so careful to hammer this information into our brain? And more importantly, what might happen if you didn't follow it to the letter? YouTube channel SmarterEveryDay put this to the test. A new video, featured on Sploid, questions the logic behind that direction we're all used to hearing on every flight: "In the event of emergency, put your oxygen mask on first." Thanks to NASA, researcher Destin was able to see for himself how vital it is to actually follow that instruction. The experience of being in a depressurized airplane cabin was replicated for his benefit (and/or terror), triggering hypoxia-like symptoms that left him weak, disoriented, and unable to help save himself. Passengers have just seconds to put on their oxygen masks before oxygen-saturation levels drop to a perilous point. By helping others first, or ignoring the mask altogether, a person will begin to lose his or her ability to recognize faces and shapes, and eventually pass out. Hence, the flight-safety demo that reminds passengers over and over to take care of their own mask right away. Watch the video, below, and wise up: Your flight crew isn't messing around.