If you share the grounds. Common grounds are necessary for reference voltage.

Yup of course! Great thanks!

Always good to think of ground as the actual ground. And voltage as how high you can reach. If we stand next to each other on the ground, one of us can reach higher (or have higher voltage) than the other.

so ground is always a reference to know the amount of voltage. Ground is also super important because if it’s not shared, or has resistance, the voltage can actually be higher - and release magic smoke.

amazing how important a common ground is. And how simple of a thing it is if it’s explained in the correct example

Great explanation!