كَلَّا لَوْ تَعْلَمُونَ عِلْمَ الْيَقِينِ
No indeed! If only you knew with certainty. (التكاثر: 5)
Law introduces a conditional clause with taʿlamūn, but its apodosis is not pronounced. The warning suggests that certain knowledge would have prevented such heedlessness. That is a reasonable contextual paraphrase, not a license to write one reconstructed sentence as though it were the only explicit wording of the verse.
This is a useful instance of ījāz al-ḥadhf: the conditional form indicates an unspoken response, while the surrounding context makes its general thrust recoverable. The ellipsis prompts the listener to complete the consequence mentally.