  An additional variation of the Einstein-Hilbert action with respect to the
Planck mass provides a constraint on the average Ricci scalar that prevents
vacuum energy from gravitating. Consideration of the evolution of the
inhomogeneous matter distribution in the Universe with evaluation of the
averaging constraint on disconnected matter cells that ultimately form isolated
gravitationally bound structures yields a backreaction effect that
self-consistently produces the cosmological constant of the background. A
uniform prior on our location in the formation of these isolated structures
implies a mean expectation for the present cosmological constant energy density
parameter of $\Omega_{\Lambda}=0.704$, giving rise to a late-time acceleration
of the cosmic expansion and a coincident current energy density of matter.
