One idea that didn't fly lead to an aircraft that did fly, and the one that didn't fly had immeasurable influence on the design of the one that did.
The boss of a certain airline had his eyes on an aircraft that was in the preliminary stages, and wanted another aircraft as an interim fill in before the other made it to service. As the interim aircraft was to be just that, he wanted it to be able to be used as freighter following its interim use as a passenger aircraft. So the aircraft projected role as a freighter dictated its design, specifically an ability to handle 8'X8'X40 shipping containers.
You may have guessed by this stage.
Boss. Juan Trippe
Airline. Pan Am
Preliminary design. SST
Interim. 747