In what situation could a fish tape potentially touch live wires?
When fishing into an electrical panel

In most cases, there will be live terminals (at a minimum, the service connections on the main breaker) in a panel you are fishing wires into.  While new panels have what are known as IP20 terminal shields that make the service terminals finger-safe (i.e the live parts are no longer poke-able with a finger), these shields are not complete protection, and are only found on very recent panels anyway.  In addition, many times when you are fishing into a panel, branch circuits not proximate to the rest of the work are left live, for obvious nuisance reasons.