Some get developed, some don’t.
This is the 1999 Dodge Charger concept car.
It was a bit funny looking, but Dodge did keep working on it, and in 2006, they debuted the production four-door Charger.
This is the 1988 Pontiac Banshee concept car.
This car never got developed. However, it did inspire the design of a fictional sci-fi car in the 1991 TV movie Knight Rider 2000.
This is the 2004 Ford Bronco concept car.
Although this didn’t end up getting developed right away, Ford is planning to debut a new Bronco in 2020, and the teaser images they’ve released look a lot like this concept. So, although it was originally a no-go, this one may actually contribute to a production car 16 years after it was revealed.