This is a very common question, and the short answer is - work hard and don't listen to your naysayers nor your lizard brain.
Starting a business doesn't require any capital, but often times many entrepreneurs aren't skillful enough to couple swagger + brute determination + insight. You have to know that it isn't about what you have, what you don't have or who you know but about how willing you are to pivot your efforts, try the same thing 3 times 3 different ways before saying that strategy didn't work, how good are you at negotiating distractions and negativity like self doubt.

I have helped several companies launch out of pure ideas and coached entrepreneurs to hustle their way to obtaining an MVP or minimal business product inventory to generate sales, in some cases you can sell before you even having a product. It all depends on the person, how likable that person is and whether or not the entrepreneur can be laser focused.

When you don't have money then you need time and clarity (that's why communities like this one here are so vital)
When you don't have time or money, then you need swagger and dedication to be everywhere, meet as many strategic potential partners as possible, learn from them, build relationships and get liked - is not about you who know but who you know and if they like you.

My name is Humberto Valle, I'm the co-founder of a global digital marketing agency (www.Unthink.me) and I have been working with startups for about 10 years and launched and exited 2 successful (no big deal though) startups myself. Best of luck, if you have any specific questions follow up and send me a message.

Do you really mean with an investment of time instead of money?

There are lots of agency, affiliate and brokerage opportunities such as travel or booking agent, freight forwarding, equipment brokerage, etc where you can earn a commission or fee from helping someone else make a sale or purchase.

What types of things do you know about that others don't? This could be an opportunity for a purchasing agent business for example.

The possibilities are endless however it's difficult to scale this type of business in a meaningful way and you may just end up creating a job for yourself. If your goal is to get out of a job you don't like by building a side hustle which can lead to a full-time thing then it may be a viable strategy.

Give me a call if you'd like to explore in a brainstorming session.

www.DavidCBarnett.com

There are several ways to start a business without any investments for instance:
1. Podcasting
Luckily, as the business continues to grow in popularity, a lot of podcast hosts are discovering many wonderful ways of monetizing their shows, including landing great deals with advertisers, and selling goods and services to their audience. In the internet marketing space, the moment you mention podcasting, one name that will always come to mind is John Lee Dumas who has built a successful business around his podcast. John hosts Entrepreneurs on Fire where he shares lots of helpful information on business and entrepreneurship. As you can see, you can start a podcast in any niche, you do not need to limit yourself to the business/entrepreneurship niche.
2. Drop shipping
You do not need a warehouse filled with inventory to run your own business. Drop shipping is a good way to start your own business on a budget without owning a single product. With drop shipping, you can run your business from anywhere because you do not need a warehouse. The guys at Shopify created a drop shipping business and generated almost $1k within 3 days of its launch.
3. Freelance Writing
Let me tell you, writing is one of the most important skills you can have as an online entrepreneur. As a talented writer, you have a lot of opportunities to build a business by offering your writing services in the form of articles, magazines, blog posts, books, editorials, etc. to busy webmasters.
4. Ghost Writing
A lot of bloggers and internet marketers are super busy with other areas of their business and do not have the time to write blog posts for their blogs. However, experienced webmasters understand the benefits of content marketing, and they know that they cannot wholly abandon it. As a ghost writer, your job is to always supply the marketer with quality content which he/she will eventually publish on his/her blog under his/her own name. A good example of someone already making a living from this kind of work is Michael Chibuzor from the Content Marketing Up blog.
5. Website Flipping
"Real estate is not the only business that involves purchasing, renovating, and selling – we also have "online real estate”. However, this one is not one of the easiest online business ideas, though it has great potential to make huge amounts of online money.
6. Online Book Publishing
Whether it is a fiction novel, a romance novel, a child’s picture story, or a marketing guide, you now have many different options for self-publishing your book.
7. SEO Consulting
Most of the website traffic today still comes from Google. It may sound like a far-fetched idea, but all you need is the internet and some zeal to learn to become an SEO expert. You can take online courses on Creative Live or find a digital marketing course which also includes SEO.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath