I must agree you need to sell items people want to buy first. If not you are not really going to make any money.
To be truely happy you need to be selling items you like and what people are looking for. I happen to be fortunate that I'm selling items I enjoy and have a market.
I was able to do this by using some
free tools to find what people are looking for in a niche I enjoy. Doing this research has allowed me to be able to do both things.
Do your research and I'm sure you will be able to do the same too.