In some complex and mature markets if you start too small you will never be able to compete with existent players. "Starting up in a garage" works mostly on new and undeveloped markets.
Depends on what you can leverage. You can start a car comapny by modifying existing cars, go up market, build a business and use the same suppliers as the other car company's. Give it 40 years and you really can start a major car company from scratch. Granted this generally takes long enough that most people fail or get bought out.
As an extreme example, before starting Tesla, Eberhard took an existing electric car [A], which was itself built on an existing kit car [B], and had a different battery technology installed [C]. And then used it as a proof of concept to start Tesla.
