Call it instinct, call it practice. Sometimes, you just know that there's a picture happening in front of you. Luckily, you have your trusty camera in your hand, you raise the viewfinder to your eye, and press the shutter, quickly, a succession of shots. Then the moment is gone. And you're so proud of yourself for being able to capture a fleeting moment, to document life as it happens, to truly represent a fragment of time, never to be repeated again.
Except, you forgot to reset your settings from the lat picture you took, so you underexposed the shot by 3 stops. Translation: Too. Damn. Dark.
Thank god we have technology these days, that recovering a photo that would have been lost in the days of film, is now a matter of a few minutes spent in Photoshop/Lightroom.
Lesson to be learned: ALWAYS reset your camera settings when shooting street.