Science is a methodically cumulative phenomenon, each advance depending upon earlier discoveries. But discoveries do not occur with methodical regularity, unlike the search for anticipated observations to confirm or refute implications of emerging theory.
The importance of unmotivated discovery at the outset of a scientific quest cannot be overstated. When discoveries in a given scientific domain are absent until late in the development of theoretical advances, those developments become increasingly distorted. There is a due time accompanying the need for every discovery in the coordinated advancement of a science, A delayed discovery presumes the absence of the associated effects and thus diverts the science away from an adequate understanding. This absence of requisite discoveries is sometimes associated with apologies for the lack of the necessary evidence to support a more reasonable explanation. This is what happened to cosmology. The missing discovery is the red-shifting effect of light transmission through high temperature plasma.