As an employee or freelancer, your money is closely related to the time you actually work. This means that time is money. Do you have a contract that indicates the minimum number of days and hours you have to work? Then you’re actually working at an hourly rate. The freelancer at a per-hour rate, and if it does not work, it does not earn, which is obviously something that causes many issues.
Here comes the power of having a product on the market: your earnings are not related to the hours you work, but to the number of products sold. If the product is digital, once you have the product finished, you do not even have a fixed cost to replicate it, so you can sell the same digital copy of the product as many times as you want.
Let’s say you spend three months writing an ebook, and you decide to sell it on Amazon. Once published, the book will be for sale forever without you having to do anything else. The same applies to a software product, excluding bug fixing and updates that introduce new features.
Certainly making the product in the first place is the most important fixed cost. You need to be reasonably sure that a product will sell, before you commit time and resources to develop it. You can’t rely on your intuition or idea that you’ve had, without having first tested it, otherwise you risk that even if your product is out there ready to be bought, no one buys it because there is no real demand.