The reasons for the growth in exotic car rentals are also rooted in the fact there are so many exotic car models from which to choose. Before Henry Ford's development of the assembly line, that made it possible to assemble simple designs efficiently and quickly, all cars were hand-built in small shops, and only the wealthy could afford them. As robotics, computer-aided design, and just-in-time manufacturing techniques now make it possible to build custom models or even unique cars on an assembly line, exotic cars can be built competitively, with high-quality components and skilled labor devoted to hand finishing.