I know that much so that to prevent electrostatic discharge we'll be better off wearing rubber gloves or using ESD bands on our wrists or hooking up our hand to a COMPUTER's metal part while we work on it.
But there's my question. There is a switch that is usually placed on the back of the desktop computer. Switch -/0. If I turn that switch to position 0 is there still a chance to cause electrostatic discharge while I'm working on a computer and happens to me not follow the rules to avoid ESD or doesn't MATTER then when the switch is positioned on 0?

My another question related to this topic. If unfortunately ESD WOULD occur what would have been affected then? What part? Motherboard, PSU, SOMETHING else?
ESD Discharge cant be solved by flipping a switch on the PC.

The destruction if any depends on what was touched at the time of discharge and the path is the shortest path to ground. So like a lightning strike forks out, wherever the discharge happens it will follow traces on the computer and fork out to other components and so it might not necessarily hurt the resistor that you touched but that resistor leg is connected to a chip that has a small junction and the junction burns out from overload. You can also have more than 1 chip blown vs just a single chip as well as a stressed junction that is partially fried to where its not quite right but no completely blown so such as on an amplifier the sound volume is no longer full volume but distorted output or not as loud as it use to be because of the damage.

Always follow proper ESD procedure to protect from damage. The wrist straps are inexpensive and work well when used properly.