You can't do one thing at once unless you do it immediately then do another. Shit and get off the pot. Do two things at once you'll do it again. I'm writing this as I listen to the radio. I'm a difficult person to know, I hear.
Any controversial proposition is dual.
An example of a bleak star is Rip Torn. You have two feet at once. When you climb the steps you can simultaneously bang the snow off your shoes, giving you more time at the door to take off your coat and say hello.