Electrical power systems are inherently dangerous. About
100 milliamps of AC current is enough to kill an adult,
far less than is needed to deliver useful amounts of power.
Electrical conductors and insulators, while very good
compared to requirements, can't be made perfect. 

It's more practical to design and build power systems
so that faults are minimzed, but not eliminated, and
those faults are promtly detected and made visible.
For example, insulation failures can connect hot wires
to equipment enclosures, but if the enclosure is grounded
properly that fault can be made to reveal itself in the
form of a tripped circuit breaker. 

Much of the rulemaking around wiring practices are meant
to constrain faults so they're either harmless (appliance
won't turn on) or obvious (circuit breaker trips). Rules
like having only a single ground-neutral bond are meant
to make faults immediatly detectable, rather than allow
existing faults to "hide" behind reduntant wiring. When
thinking about your wiring, play out the possible scenarios
of intended connections accidentally opening and intended
insulation shorting, either partly or completely. All the
possibilities should ideally result in a prompt, harmless
fault. At minimum, any stray voltages must remain out of
casual reach. 
 

The problem of partial failures, either bad connections
or smallish current leaks, is much harder to detect and
manage. Bad connections on hot wires usually cause poor
appliance performance, but resistive neutral wires can
be very hard to detect until the neutral is so badly
out of balance that loads start to misbehave.