If you have a hard time coming up with ideas, you probably shouldn't start a company.
This really comes out in corporate mission statements. Even if you're Xerox, your mission statement is something like "Improve the rate of business communications by creating the world's most excellent copy machines."
If you don't have an idea for a startup, you're missing the key ingredient. The team literally cannot exist without that visionary person who knows exactly what they're after.
I could not disagree more. Companies are started by all sorts of people: some founders have a definite idea that is a perfect fit for the market(Stripe,Heroku), some go over many iterations of their original idea and may even end up abandoning it for something entirely unrelated(Reddit), the last type of founder simply wants to be in business and does not even know what his product is yet(Steve Jobs before he joined Pixar). The only trait all founders share is drive and ambition.