Star Trek: TOS — The Cage The Show That Almost Wasn’t (Pilot)
“Too cerebral” was the phrase NBC used when they sent it back. As criticisms go, it has aged badly for them.
Desilu delivered a science fiction pilot in 1965 that was slower, stranger, and more introspective than the network knew what to do with. They wanted something else. What came back was Star Trek as most people know it: Kirk, action, adventure, and the formula that would carry the franchise for decades. The original pilot went into a vault. Most people never saw it.