Garrote Question

[Rhino]

“A garrote is a cord or wire used for strangling. You can use it only to attack unaware or helpless prey – and only from behind. You must target the neck at -5 to Garrote skill. Consider risking an All-Out Attack (Determined) for +4 to hit! Your victim may attempt to parry with a hand or close- combat weapon at -3. During a surprise attack (pp. 26-27), mental stun gives another -4 to this parry.”

If the garrote can only be used against a helpless or unaware opponent, how does the helpless or unaware opponent ever get an active defense?