Lightning (번개, beongae) is read as sudden, dramatic change — for better or worse — and Korean already has a phrase that makes the positive version of this reading explicit: 벼락부자 (byeorak-buja), literally "lightning-rich," describing someone who becomes wealthy overnight. A dream of lightning striking near you, without harming you, taps directly into that expression.
Lightning that strikes and causes visible damage shifts the reading toward sudden misfortune or a shock — an abrupt, unavoidable event rather than a gradual one. The suddenness is really the whole symbol here; lightning doesn't build slowly the way a storm does, and the dream is generally read the same way: something arriving all at once, without warning.
Seeing distant lightning light up the sky without any sense of danger is read more gently, closer to a flash of insight or sudden clarity than an event happening to you directly — a reading that overlaps comfortably with the ordinary English idiom of a "lightning bolt of realization."
Being personally struck by lightning is the most intense version, and traditionally read as an overnight transformation — dramatic enough that most interpreters treat it as one of the more significant dreams in this entire category, regardless of which direction (fortune or misfortune) it ultimately points.