Asteya looks like the easiest yama, since most people are not thieves. The commentarial tradition spent its effort closing that comfortable loophole. Steya, stealing, is defined in Vyasa's commentary as the unauthorized appropriation of things belonging to another, and asteya as the refusal of that appropriation even in the form of desire. The last clause does the work: the yamas restrain thought and word as well as deed, so coveting is already a lapse, and the vow is broken in the mind long before anything is picked up. From there the tradition widens the inventory of what can be stolen. Time can be stolen, by the idle consumption of another's labor.
Credit can be stolen, by claiming work one did not do. Opportunity can be stolen, by hoarding beyond need while others lack, an argument that brings asteya to the edge of aparigraha, the non-possessiveness that follows it in the list. Jain ethics, holding the same vow as the third mahavrata, adds its own refinements: a mendicant may not take even a blade of grass that has not been explicitly given, and adulteration, false weights and dealing in stolen goods are enumerated as lay violations. What began as a prohibition on theft becomes, fully unfolded, a discipline of taking nothing, materially or subtly, that has not been freely offered.