Is how everything is only set in motion by the one singular act of selfless charity/empathy that takes place in the entire movie: Llewellyn going back to give the dying Mexican his agua.

Llewellyn had the money safely hidden away under his trailer. Nobody knew he had it. The site of the drug deal was far enough away from town that there is virtually no way the Mexicans or Chigurh would have found him using the beacon, at least before Llewellyn eventually found the beacon and discarded it. It was only because he drove back to offer a dying man some water that the Mexicans were able to chase him. That of course enabled Chigurh to later get his plates after the Mexicans had slashed his tires. And to cap it all off, the dying man was already dead; Llewellyn's empathy was wasted from the outset.

None of the bad things that happened would have happened if Llewellyn hadn't been selfless, and instead had simply hoarded the money for himself. To me, that sets the tone for the whole movie.