After all, you're going to be putting a whole lot of time and energy into realizing your goal of creating your own income, and not being a slave to someone else. So you might as well enjoy what you do.
Apart from the pleasure that this activity gives you, your clients will pick it up as well -- particularly if your business involves a lot of human contact. It's just so much more fun dealing with people who are enthusiastic, and aren't just doing it for the money after all. If your customers sense this, odds are they'll recommend you to others too.
Now, if there's a huge and constant demand for that thing that you find so fulfilling, you're pretty much home and hosed. If there isn't it's obviously going to present some challenges. But I don't think these are insurmountable in most cases.
As long as you've got something that some people need and are willing to pay for, the challenge is to find where they are and advertise to them. Then you've basically got to get your advertising costs down low enough that you're making a profit -- even a small one. Then you rinse and repeat, refining it all the time.
This is obviously a long process. That's why having a passion is so important. It will keep you going until you do find a way to make your venture profitable. If there's no passion, you'll give up pretty quickly.
Here's an example from my own experience: As a result of promoting this very site and its attendant services, I've realized that there's a huge demand for people seeking help with computers. They need them fixed cheaply, and many have emotional issues with them and feel they need someone to patiently guide them through using them so that their fear goes away. I could easily make much better money than I am now if I choose to offer both, or either of these services. I won't, however, because I'm neither a geek nor a social worker!
My passion lies in blogging, drawing traffic via search engines, and social media usage. And I enjoy teaching people key concepts about these practices. This is a smaller, narrower market than the computer troubleshooting and instruction described above, but it's definitely out there.
I know this because I have slowly been building an income offering these lessons. I'm not saving anything but I am getting by, just. And I can see what I need to do in future both short and long term. There's no reason I can't increase my income by about a third in the next six months. If I manage to do that I'll be laughing.
Having a passion is also particularly important to the online aspects of promotion. That enjoyment of and keen interest in what you do is what will supply you with so much unique content that you can put in blog posts and be found by people who might ultimately buy your services. You can share it on social media, too, thereby building substantial authority on those sites.