What NBC could not fully see was the specific audience that the show was building. The Nielsen ratings system of the 1960s measured viewership by household, using a methodology that was designed around the established television audience of married couples and families watching in the evening. *Star Trek*’s audience skewed toward young people, college students, and individuals who watched alone — demographics that the Nielsen methodology of the era was not well equipped to capture and that were not, in the mid-1960s, understood as the most valuable advertising audience.
The show’s specific appeal to young, educated viewers was not invisible to everyone at NBC. Some advertising buyers understood it. Some affiliate managers in college markets reported strong local performance. But the aggregate national ratings number was what drove network decision-making, and that number was consistently in the middle of the pack — good enough to avoid immediate cancellation but not strong enough to justify scheduling priority or promotional investment.
The scheduling decisions NBC made — including the Friday 10 p.m. death slot in the third season — reflected a network that had exhausted its enthusiasm for a show that wasn’t delivering the numbers they had hoped for. The fan campaign that had generated hundreds of thousands of letters had produced a renewal, but it had not produced a conviction at NBC that the show was commercially viable at the level that would justify investing in its success.
The subsequent history suggests that NBC was making a measurement error rather than a value judgment. The show that NBC’s ratings system said was a marginal performer in 1968 was the show that syndication turned into a cultural phenomenon in the 1970s. The audience NBC couldn’t fully see was the audience that showed up in reruns and refused to leave.