 The physical conditions necessary for our existence impose a selection effect on what we observe. The significance of this point for cosmological theorizing is exemplified by Dicke’s criticism of Dirac’s speculative “large number hypothesis”. Dirac (1937) noted the age of the universe expressed in terms of fundamental constants in atomic physics is an extremely large number (roughly \(10^{39}\)), which coincides with other large, dimensionless numbers defined in terms of fundamental constants. Inspired by this coincidence, he proposed that the large numbers vary to maintain this order of magnitude agreement, implying (for example) that the gravitational “constant” \(G\) is a function of cosmic time. Dicke (1961) noted that creatures like us, made of carbon produced in an earlier generation of red giants and sustained by the light and heat of a main sequence star, can only exist within a restricted interval of cosmic times, and that Dirac’s coincidence holds for observations made within this interval. Establishing that the coincidence holds at a randomly chosen \(t\) would support Dirac’s hypothesis, however slightly, but Dicke’s argument shows that our evidence does not do so.