Selling on Amazon isn’t the only way to generate positive cash flow. You might have heard of the saying “sell shovels in a gold rush.” That’s exactly what Amazon affiliate programs are. Instead of going through all the work to sell on Amazon yourself you could be selling the software Amazon Sellers are looking for to better their lives and save them time. 
The topic you choose must have enough depth that you can create a lot of content for it. This is important for building an authoritative site, for search engine optimization, and most importantly, for the end user. If you don't have enough content about a topic, you're not going to be taken very seriously as an authority on the topic and it's unlikely you can convince someone to make a purchase from you.