A Room of One's Own
In her 1928 essay of the same name, Virginia Woolf argued that, "A woman must have money and a room of her own if she is to write fiction."
To the same extent, I think the same thing applies to entrepreneurship. Most entreprenuerial dreams die an early death because they are starved of the most precious resource: Time. I can attest to this fact from personal experience; with two small children under the age of 3, I can barely find time to keep up with a real job, let alone work on a new entrepreneurial idea (though I have several, and if you are looking for an idea and an advisory board member, drop me a line!).
An entreprenuer needs money and a room of her own to efficiently and quickly create a company. In my own mind, I've done a hypothetical analysis, and concluded that if I did not have to work a job, had my own office, and $50,000 per year to spend, I could start one new business per year.
Thanks to the relentless progress of Moore's law and the death of distance, it is orders of magnitude cheaper to start a company. I can incorporate online for about $150. I can get a corporate identity designed by Romanian freelancers for $100. I can get an entire custom e-commerce back-end built by Indian programmers for less than $10,000. All of those would have cost 10, 100, or even 1,000 times as much during the pre-Internet era.
I hope that in the not too distant future, I will be successful enough to own my own home, have enough money to pay my living expenses and spend $50,000 per year on business startup expenses, and have the time to be serial entrepreneur. And if you already have those things, what's your excuse? Get out there and create!