Much of the broadcast schedule was simply too valuable to be left to chance. Experimenting with a few stations and high ideals might have their place when sponsorships were the norm, when nothing could be accurately measured, and all was a matter of feel, but now, by the late 1950s, every moment of what was called prime time had both fixed costs and a revenue potential to be met or brutally aspired to.

Tim Wu, The Attention Merchants, loc. 491