7 Audacious Startup Ideas That Eventually Became Wildly SuccessfulRocketships. An online bookstore. The 'Pet rock.'. What crazy idea do you want to pursue?

Startups often grow in unexpected ways. An idea you thought was a surefire win may turn out to have a weaker client base than you thought; or an idea with significant backing through crowdfunding might not have enough money to keep going.

On the other end of the spectrum are startup ideas that sounded crazy when first conceived, but somehow managed to become successful anyway.

Related:The 10 Best New-Age Business Ideas You Haven't Heard About Yet

Take inspiration from these examples:

1. The Pet Rock

I'll start this list with a classic example:the Pet Rock．Back in the 1970s, Gary Ross Dahl came up with an idea to sell rocks to children, under the premise that the rock was some kind of pet. A combination of clever packaging and brilliant marketing made the concept of paying for a rock seem much more reasonable; and, eventually, the idea made Dahl a millionaire.

2. PayPal

Today, millions of people rely on PayPal to handle their financial transactions, trusting it as much as any bank (if not more so). Butback when PayPal launched in 1998, it was pushing into a bold new frontier. The internet was still new and commanded little public trust, yet PayPal's co-founders expected you to hand over your bank account information, along with other personal info, and trust that they could handle your financial transactions online.

3. Instagram

Instagram was founded back in 2010, during an era when Facebook was already the king of social media. The platform actually emerged as a Foursquare knockoff, but started to gain popularity when it switched to a model that consisted almost entirely of sharing images with your friends, family and other followers.

Aside from filtering functionality and focusing on mobile devices, Instagram wasn't uniquely different from its competitors, yet it managed to cultivate a strong initial user base. It has now grown to become one of the world's most popular social media platforms, with more than800 million monthly active users．

4. Github

Githubmay seem complicated to non-programmers, but since its inception, it has grown into a massively powerful tool (and open community). Today, it's the largest host of source code in the world, but when it started, its premise was ludicrous: Software engineers would need to pay a monthly fee to use open-source code to create more open-source code?

The model works, however, as24 million dedicated GitHub userscan attest.

5. Slack

On the surface, Slack didn't offer anything new. Companies already had email platforms or project-management apps to help them communicate with one other and manage products; Slack was just another tool in the tool belt. But Slack's creators noticed that70 to 80 percent of companiesdidn't have a designated tool for internal communication, so they decided to market themselves to fill that gap.

After gradually scaling up to different team sizes and offering integration with dozens of other tools, Slack grew to become a billion-dollar company.

6. SpaceX

When SpaceX started back in 2002,nobody took it seriously．美国宇航局the only organization that had attempted to design or launch space-related technology and no private companies had attempted to do things better. Then came SpaceX. And, indeed, after failed launches and new rounds of investment in the early-to-mid-2000s, the company's prospects looked grim.

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But after some successful launches and major contracts from NASA, SpaceX started generating momentum, in the early 2010s. Today, Elon Musk's company is producing some of the most cost-effective and practical space-related technology we've ever seen.

7. Amazon

Few companies have churned out as many audacious ideas as Amazon; even now, the company is attempting to build a future with automated drone delivery and smart speakers controlling our homes. But the most audacious idea may have been the one that started it all:selling books online．

It seems intuitive now, but back in 1994, buying books online was considered risky; how could you guarantee that you'd get what you paid for? And, besides, there were bookstores in every major city. Why not simply buy a book from them? The idea, however, was sound; books were in high demand, they were inexpensive and they were easy to ship. What seemed nonsensical was actually brilliant. In a matter of years, Amazon became one of the most popular sites on the internet and started expanding to offer products that went way beyond mere books.

Related:25 Business Ideas Worth Millions That I Don't Have Time to Build

Did these audacious ideas succeed in part because of their sheer boldness and innovation? Or were they driven to success by uncompromising founders who were willing to make big sacrifices to make them successful?

Either way, these successful startups are evidence that even the craziest idea has a chance to be successful, so long as it's built with the right foundation. Take inspiration from these concepts and leaders andgive your most audacious ideas another shot at success．