When I started learning about electrical engineering, one of the most important safety guidelines that I learned was that voltages over 36V can be dangerous. As my circuits professor put it, 120VAC will sting, and 240VAC will seriously hurt.
Now that I know more about these voltages and their dangers, I'm confused about mains electricity and how safe it is. I often see people (un)plugging power cables into outlets that are behind a desk or a couch without a clear view of what they're touching – sometimes with two hands to get a better grip, a definite no-no in my electrical labs at school. How dangerous is the risk of, for example, touching a finger across both the hot and neutral lines? Do the circuit breakers in a home really guard against this, or is 120/240VAC not quite as dangerous as I think?