Your blind spots move around when you're performing a manouvre, and you have to look in several directions at once while concentrating on the task you're performing, so if a small visual target (e.g. a cyclist) is also moving around in your blind spots, your chances of seeing them is much lower. Always gobsmacked at the number of cyclists who see a gap in the road while a vehicle is performing a manouvre and think "I can fit through that! WAHEY" without paying any attention to which direction the car is moving in and whether the driver has seen anybody else there.
^ This, always
Your blind spots move around when you're performing a manouvre, and you have to look in several directions at once while concentrating on the task you're performing, so if a small visual target (e.g. a cyclist) is also moving around in your blind spots, your chances of seeing them is much lower. Always gobsmacked at the number of cyclists who see a gap in the road while a vehicle is performing a manouvre and think "I can fit through that! WAHEY" without paying any attention to which direction the car is moving in and whether the driver has seen anybody else there.