Some shows often are a victim of their own successes, such that either the network, or, at the time of our next subject, a sponsor might have some issues that result in the show going off the air.
One such case is Tightrope, a half-hour Screen Gems crime drama that crammed nearly 40 episodes into its only season (1959-60), and made a star out of Mike Connors, eight years before he would land an even bigger success with Mannix.
Connors played an undercover cop, whose assignments often resulted in fellow officers being kept in the dark. Connors narrated each episode, much like Richard Diamond or Dragnet. Unfortunately, it's long been off the air, though I suspect that Sony-owned Get TV might get its hands on it sooner rather than later to reintroduce the series to a new audience.
Take for example the episode, "Getaway Day". How many familiar tropes can you find?
So why was it cancelled? The J. B. Williams Company, at the time the makers of Aqua Velva & 'Lectric Shave, objected to CBS moving the show to a later time, and Connors also had issues with rumors of the show being expanded to an hour and adding an unnecessary sidekick.