But heres the catch: If you connect the circuit wires to the wrong terminals on an outlet, the outlet will still work but the polarity will be backward. When this happens, a lamp, for example, will have its bulb socket sleeve energized rather than the little tab inside the socket.

Does it matter how you wire a light switch?

With a switch loop yes, it should. The hot wire should come down from the ceiling on the white wire and go back up on the black wire. Just think white down, black up. If you wired it the other way around, hot black down and hot white up, you have a problem.

Why does my light switch have two black wires?

The bare or green-wrapped ground wires serve as a backup to divert the power safely away in case of an electrical fault. In most cases, two black wires will be attached to the switchs two terminal screws. The ground wires will be connected to each other and attached to the grounding screw on the switch.