The discussion centers on the significance of the expression (p.r - Et) in the context of special relativity (SR) and its relation to the concept of action. It highlights that this expression represents the Minkowski inner product of four-vectors and is Lorentz invariant, suggesting a deeper connection to the principles of both non-relativistic and relativistic quantum mechanics. Participants debate whether this mathematical relationship has physical significance, with some asserting that it is merely a coincidence while others suggest it relates to the fundamental invariant of action. The conversation also touches on the nature of the Lagrangian and its role in defining physical laws across different frameworks. Ultimately, the consensus leans towards recognizing action as a central invariant in both classical and quantum physics, linking various physical phenomena.