Likely influenced by the Chinese adage 没死过，你不懂, méi sǐ guò, nǐ bù dǒng, ("@{never die before, you don’t know"), implying that one has to go through a severe scare or near-miss to learn a harsh but important lesson — from which the conclusion that one will 'then know' after facing the consequences naturally follows.
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definitions
expression
used to caution someone against a course of action (or inaction) in light of the possible and/or likely consequences
Always so last minute go airport one… Later the plane leave without you, then you know.