This is often the most common method people think of when it comes to making money online. In fact, many people think it's the best way to earn a solid, long-term income.
I do agree that it can be the most lucrative approach, since having your own product means you directly control how much profit you make.
However, there can be some headaches with this method. For example, you are in charge ofeverything. Selling your own product means you are responsible for customer service, collecting orders/payments (credit cards), developing and shipping the product, etc.
Note: Thanks to companies like PayPal and WordPress plugins, collecting payments is no longer the headache it used to be.
In addition, it's usually a good idea to setup some kind of business name, although it is not necessary.
Selling a product can be a lot of work, especially if you're new to marketing. However, once those sales start rolling in, you can build a steady, long-term income.