Studies show that if a man meets a woman in a dangerous situation
(and visa versa), they are more likely to fall in love.

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The Suspended Bridge Effect, or Misattribution of Arousal, is a term in psychology which describes the process whereby people make a mistake in assuming what is causing them to feel aroused. For example, when actually experiencing physiological responses related to fear, people mislabel those responses as romantic arousal. The reason physiological symptoms may be attributed to incorrect stimuli is because many stimuli have similar physiological symptoms such as increased blood pressure or shortness of breath.

TLDR:
Two people on a high bridge are super scared but when (for example) they are reassured by the other person they think "Could this be love?"