>>2952336
>Will I die if I do this or do I have to learn how transistors/relays work

My pallet stacker literally works on this exact principle, except it has multiple switches and relays for different speeds. It's far from an efficient method of control, but it works. Definitely not worth it when you can get a basic motor controller and throttle for so little. Certainly less than the enormous variable resistor you'd need to handle enough power to get a bike moving.