Extremely fast or happening in an instant.
This simile dates back to the mid-19th century, comparing speed to a flash of lightning, which was one of the fastest observable phenomena before modern technology. The phrase gained popularity as photography developed and camera flashes became common, reinforcing the association between 'flash' and instantaneous action.
Before electric lighting, a flash of lightning was literally the fastest thing most people would ever witness, making this comparison incredibly vivid and relatable. Interestingly, we still use this phrase even though we now have many faster references available - it shows how linguistic metaphors can outlive their original technological context!
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