A control system with a pole (in the control systems sense) in the right hand half of the plane will be unstable. If the system changes during operation, the po

A control system with a pole (in the control systems sense) in the right hand half of the plane will be unstable. If the system changes during operation, the pole can move around the coordinate plane.* As it goes from the left (stable) towards the right (unstable) the system will begin to oscillate as the pole crosses the Y axis. In the joke, a Pole (person of Polish origin) was in the left of the (air) plane. When they crossed the aisle to look out the window, the (air) plane became unstable and crashed (pole in the right hand plane). *My control systems professor loved to explain using an example of a driver as a control system. The system (car + human driver) seeks to minimize error against the lines on the road. If the driver starts drinking, one of the system's poles will move right. The car will start overshooting first, then will start weaving, before finally crashing when the driver is too drunk.