If you don't practice this and commit it to muscle memory *before* you're in an accident or floating in a pond, you will not 1) read the owner's manual, 2) figure it out 3) and calmly execute the procedure, all while you're in an emergency situation.
You don't have enough time. You could have only a minute or so before the car is either engulfed in flames, or completely submerged in water. You might be concussed or disoriented. And adrenaline dumps reduce coordination.