The goal of circuit-breakers and grounded cases is to remove any long persisting situations where the metal case was already dangerous when a human touched it.
If you pick up an ancient all-metal electric drill with a 2-prong cord, where the Line conductor has contacted the metal case weeks ago, nothing will happen ...until you step into a pool of water in the basement, or lean on a steel kitchen sink, or grab a metal conduit for balance, etc. Now your body is unexpectedly connected between Line and earth/neutral.
But still you aren't in serious danger, since you'll probably yell YOW!!! and yank your hand away from the earthed surface, or perhaps drop the drill, breaking the circuit.
For less lucky people, the lethal danger is from "clamp on," where the current through your body causes your muscles to push harder onto the electrically-live metal case or grounded object. With the above power-drill, when stepping into a saltwater pool, your hand may grip it hard, and your arm-muscles also freeze, so you cannot shake it free. (For lucky people, their arm muscles contract, violently flinging the power-drill across the room!) During clamp-on, the current may interfere with breathing, so, if you cannot fall to the floor in order to pull loose, you'll slowly die of suffocation. If the path is through your chest, the current may interfere with heartbeat (either immediately for a weak heart, or, since the heart is quite shielded by surrounding tissues, much time may be required before skin conductivity increases at the contact points, the fault current increases, and eventually your heart cannot beat normally.)
Search for electrocution and "clamp on."
The OP question is about a live-enclosure fault which happens while the user is both touching the case, and also is securely connected to Earth (e.g. grasping a faucet with the other hand, etc.,) and ALSO, either the current-path is across the chest and ALSO they have a serious heart condition where a half-second 120VAC shock is lethal rather than just surprising ...THAT, OR they encounter "clamp-on" and suffocate over ten minutes of constant shocking.
Obviously the grounded case and blown breaker removes the last danger.
Heart-attacks caused by brief encounters with 120VAC during the time before the breaker blows: they remain a (rare) instance which could be avoided by that special device sold in the 1970s which detects tens of microamps of ground current, and then "blows the breaker" within a half-cycle of 60Hz, using active electronics.
That 2-prongs world of our ancestors:
thirty electrocutions thirty (from 1930?)