I'm not arguing that the throttle or mixture / propeller controlls don't also have balls, which is what their picture's demonstrate though...

I'm arguing that the origin of the phrase comes from military aviation, where diving in order to gain speed involved moving the control column towards the firewall (one ball) and also the throttle towards the firewall (the other ball), and this lead to the phrase "balls to the wall":

https://www.quora.com/Where-did-the-phrase-balls-to-the-wall-originate

> Another control is the joystick—pushing it forward sends a plane into a dive.So, literally pushing the balls to the (fire)wall would put a plane intoa maximum-speed dive, and figuratively going balls to the wall is doingsomething all-out, with maximum effort.

*edit formatting*