Describes someone who is cunningly alert and never misses an opportunity; often used in contexts like big-city survival or competitive environments. The literal image is of plucking out a live horse's eye—an act requiring extreme speed and audacity.
東京は生き馬の目を抜くような街だ。
Tokyo is a city where you have to be sharp and keep your wits about you.
He is a shrewd businessman who never misses a trick.