Satya is built on sat, the present participle of the Sanskrit verb to be. Truth, in this construction, is not primarily a property of statements but a fidelity to what exists: the true word is the one that stays with being, the false word the one that departs from it. The oldest strata of the tradition already exploit the connection. The Rig Veda pairs sat against asat, being against non-being, and the famous Upanishadic prayer asks to be led from asat to sat, from the unreal to the real, making truthfulness continuous with the whole religious project of moving toward reality.
The Chandogya Upanishad's refrain tat tvam asi rests on the same root: what you ultimately are is sat, being itself. Against this background the yama acquires depth. Lying is not merely a social offense; it is a small secession from reality, a private counter-world maintained at the cost of contact with the real one, and the yogin, whose entire discipline aims at seeing what is, can least afford it. Patanjali's promised fruit at sutra 2.36, that for one grounded in satya actions and their fruits follow the word, reads naturally in these terms: speech that has never departed from being acquires the reliability of being, and the tradition's tales of sages whose word cannot fail to come true are this promise told as story.