Have you ever played pinball? If yes, you may have run into the situation where you have to deal with two or even three balls on the field at the same time. Your attention constantly moves from a ball to another and this can work for few minutes but then, one after another, the balls fall into the drain. Game over!
The reason is simple: our brain is not able to work in multitasking mode. Stop playing and back to work! How many times are you asked to switch from a task to another? There is this urgent bug to fix, that small feature for a big customer to implement quickly, etc. Then you work a couple of days on a big project and stop on a urgent task. And while you are in the middle of this task - guess what? - another interrupt. And while you are addressing this, the first one promptly become there most important. Just like the pinball, as soon as one of the balls arrives close to the flippers, you have to take care of it.
But the similitude with the pinball doesn't end here. You cannot sustain this continuous context switching indefinitely. Soon or later you'll make mistakes, forget something or make some mess. Managing several tasks at the same time is possible but it comes with some costs. Are you (and your company) ready to pay?
Image by ElHeineken taken from Wikimedia Commons licensed under the Creative Commons Attribution 3.0 Unported license.