I experienced that multitasking was an illusion

At Adobe we had a session consisting in packing meals for starving people.
The office became a big assembly line.

We all had specific tasks we were repeating as fast as we can, optimizing each gesture.
Each time someone started chatting, each time someone started watching something else than his task, he made mistakes.

Worst, each time it took him a couple of seconds to re-focus.

Terrible proof that multitasking is an illusion.