An engineer who doesn't understand math — I don't see how that works.
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From the Analects 《论语·为政》: ‘人而无信，不知其可也。大车无輗，小车无軏，其何以行之哉？’ (If a man has no trustworthiness, I do not know how he can get on; like a large cart without a yoke-bar or a small cart without a cross-pin — how can it move?) Confucius's foundational statement on 信 (trust).
usage
可 here = permissible / workable (classical), not ‘can.’ Always follows 人而无信 in citation.
