I'm new to electrical engineering, and I still have many stupid questions. Here's one of them.
This is what I'm reading. https://itp.nyu.edu/physcomp/labs/motors-and-transistors/using-a-transistor-to-control-high-current-loads-with-an-arduino
Next, add a diode in parallel with the collector and emitter of the transistor, pointing away from ground. The diode to protects the transistor from back voltage generated when the motor shuts off, or if the motor is turned in the reverse direction.
I thought before that polarity could be reversed in transistors, but now I'm confused. Can it not be? Why would it hurt the transistor, and how would it? Would it instantly break it? How does doing this fix it?
-edit to defend not being duplicate-
The proposed duplicate does not answer my question because it does not give how the transistor is affected. From searching online, I couldn't find this either; I'm probably searching the wrong thing. It also does not answer whether it is instant or how it fixes it.