My key is stolen. I have to revoke it, but I need my duplicate to log in to do it. The attacker stole my key and phone, because they were in the same place. I've only got a few minutes to go out to the remote forest and dig a meter down to find my key before the attacker uses it with the phone back at bad guy headquarters to launch the nukes. Did I bury it next to this tree or that one? Damn it, they all look the same now. Dig fast, but careful not to smash the key with the shovel. Gosh, the water table is higher than when I buried it. I hope it still works. Christ, it's all tangled in roots! Pull!! Got it! Now log in, revoke it, reflash the key, re-enroll. Phew! Humanity is saved.

With PKI, I contact my spouse. Honey, can you revoke the key I'm carrying? It's been stolen. Thanks sweetie! See you tonight.

I'll admit the duplicate approach makes for a much better movie. The PKI solution is positively boring. Maybe we could throw in a spouse kidnapping to keep it interesting?