The biggest challenge is to build the team and start the company, while hiring people, raising money, building a brand which has no history, all at the same time. You're doing a lot of things that in an established company are already done.
My motivation for starting Fisker was simple: I thought there must be a market for beautiful, exciting, fast, environmentally friendly cars. The car is probably the only product you can still fall in love with and have a relationship with.
Any car designer always dreams about designing their own car - if they say they don't, they're lying... For me, it was never about starting my own company just to make another car.