ISO sensitivity
ISO sensitivity is the epic tug-of-war between a photographer's ego and the harsh reality of available light. Turn it up, and even darkness appears bright—but at the cost of adorning the image with merciless speckles called noise. It is like an artist seeking maximum self-expression while being criticized for quality loss. For believers it's a holy grail, for skeptics a curse. Yet people continue to tweak the numbers every day, chasing the perfect shot.