Answer by Michael Wolfe, Five startups and counting, on Quora

The best startups seem obvious only in retrospect. By the time most of us found about them, they had already reached a critical mass of users. We never had to ask the question "Will this work?" since we already saw it working.

It is possible to create a "good" startup with a "good" idea, but "great" startups are often the result of ideas that would have seemed ridiculous if you had heard them prior to seeing them working. This is true almost by definition--if they had been so obvious, lots of companies would have already been doing them.

Ask yourself, if you were a venture capitalist pitched one of these ideas, what would your reaction have been?

1. Facebook

The world needs yet another social network a la MySpace or Friendster except several years late. We'll only open it up to a few thousand overworked, antisocial Ivy Leaguers. Everyone else will then follow, since Harvard students are so cool.

2. Dropbox

We built a file-sharing and syncing solution in a market that has a dozen of them built by big companies like Microsoft. It has only one feature, and you have to move all of your content to use it.

3. Amazon

We'll sell books online, even though users are still scared to use credit cards on the Web. Their shipping costs will eat up any money they save. They'll do it for the convenience, even though they have to wait a week for the book.

4. Virgin Atlantic

Airlines are fun, so we are starting one. How hard could it be? We'll differentiate with a funny safety video and by not being a--holes.

5. Mint

Give us all of your bank, brokerage, and credit card information. We'll store it on the Web and give you the data back but with nicer fonts. To make you feel richer, we'll make it all green.

6. Palantir

We'll build arcane analytics software, put the company in California, hire a bunch of new college grads, many of them immigrants, hire no sales reps, and close giant deals with D.C.-based defense and intelligence agencies.

7. Craigslist

It will be ugly. It will be free. Except for the scammers and hookers.

8. iOS

We are shipping a brand-new operating system that doesn't run a single one of the millions of applications that have already been developed for Mac OS, Windows, and Linux. Apple has to approve all of the apps, and it won't have cut and paste to start with.

9. Google

We are building the world's 20th search engine at a time when most of the others have been abandoned as commoditized money losers. We'll strip out all of the ad-supported news and portal features so you won't be distracted from using the free search stuff.

10. Github

Software engineers will pay monthly fees for the rest of their lives to create free software out of other free software.

11. PayPal

People will use their insecure AOL and Yahoo email addresses to pay each other real money, backed by a non-bank with a cute name run by 20-somethings.

12. Paperless Post

We are like Evite, except you pay us. All of your friends will know that you are an idiot the minute your faux-parchment digital envelope hits their inbox.

13. Instagram

Who needs Facebook? We got filters! That's right, filters!

14. LinkedIn

How about a professional social network, aimed at busy 30- and 40-somethings. They will use it once every five years when they go job searching.

15. Tesla

Instead of just building batteries and selling them to Detroit, we are going to build our own cars from scratch plus own the distribution network. We'll start the company during a recession and the crashing of the clean tech industry.

16. SpaceX

If NASA can do it, so can we! It ain't rocket science. Oh, it is.

17. Firefox

We are going to build a better Web browser, even though 90 percent of the world's computers already have a free one built in. It's based on a product that a single college student built.

18. Twitter

It is like email, SMS, or RSS. Except it only has 140 characters, doesn't support images, can't be made private, and will be used mostly by geeks at first, followed by Britney Spears and Charlie Sheen.

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