Many startups begin as passion projects, which naturally means that some of those ideas are pretty crazy--and some of them actually work. If you have an idea that you know is a bit kooky, but you think others might see it for the magic it is, don't let fear of what other people say hold you back. If you did, that would make life (and business) pretty boring. Sometimes you'll find good company and loyal customers with the most outlandish ideas. Here are a few of the wilder startup ideas that worked.

1. Pet Rock

This product just got a revival in 2012, and it definitely proved successful enough for Gary Dahl in the 1970s. Dahl was at a bar listening to friends complain about their pets in 1975 when he came up with the idea of a pet rock--the perfect, easy-to-care-for pet. This craze ended up with a 32-page training manual, detailed care instructions filled with jokes and gags, such as commands like "playing dead." It was incredibly cheap to produce (the rocks cost just a penny each). Dahl ended up $15 million richer.

2. Narrative Clip

This product is a tiny camera that clips to shirt fronts and takes two photos per minute as long as it's worn. Now, you might think that sounds useless, but there are a lot of people who would disagree with you. The folks behind the Swedish startup are claiming it's the only way to actually relive your life. It costs $279 and the company has already earned half a million on a Kickstarter campaign. It's a literal way to leave your legacy behind.

3. Facebook

Too kooky to work. That's what some people told Zuckerberg about his idea when he first launched an "exclusive" virtual yearbook. Certainly nobody thought it would become one of the most powerful companies in the world. Think about it: What's the point of a virtual yearbook when there's already a giant, well-loved social network called MySpace? The exclusivity factor worked, as did the more mature layout, and the rest is history.

4. Craigslist

Craigslist hasn't changed since the day it was launched, and people love it for its ugly simplicity. People criticized it, citing privacy and safety concerns, once upon a time. Founder Craig Newmark has never made revenue priority number one for the site. However, Craigslist is going stronger than ever. It's where you really can get almost anything; whether it be a job, apartment, girlfriend, casual hookup, or entertainment on the forums. A free community that's a veritable garage sale of sorts? It still works today.

5. PayPal

It's kind of crazy to think how trusting the first PayPal users were. They handed over their bank account and email information to a company that was in no way affiliated with a bank and had kind of a cutesy name. Would PayPal have been successful if launched at any other time in history? Who knows, but the founders definitely found success amid a consumer lack of tech savviness specific to the late '90s, along with a healthy dislike of dealing with mailing checks. This kooky idea helped push some great investors and entrepreneurs to the forefront, including Peter Thiel and Elon Musk.

6. Amazon

This is another example of a company that was way ahead of its time. Who wants a virtual bookstore when you can go to Barnes & Noble or Borders? Many an American can remember countless hours hanging out in one of those, drinking a coffee and reading magazines and books (for free!). As it turns out, a lot of people wanted a virtual bookstore, and brick and mortar stores weren't happy about it. Never underestimate the appeal of being lazy in your pajamas at home.