Why is it so difficult to swat a fly?

Attempt to swat a fly and it will soon turn out to be evidence that they're quicker than you. Substantially quicker. Be that as it may, how on Earth do these little animals - with their minute brains - outsmart us so effortlessly? 

Roger embeds little glass cathodes into the living light delicate cells of their eyes - photoreceptors - before blazing Drove lights at quicker and speedier rates. Each blaze of the Drove creates a little electrical current in the photoreceptors that a PC can chart onto a screen. Tests uncover the speediest fly records unmistakable reactions to glinting up to 400 times each second, more than six times speedier than our own particular rate.