Most people wait until they receive a thunderbolt idea that's going to change the world. Or they start with an idea so big and complicated, it's like trying to do an iron man of swimming, running and cycling when you can't walk around the block.
So, they either never start because they have no idea, or they give up because they don't have the training and 'business skill strength' to complete that marathon.
When you realise that building a successful and long term business requires you to build strength in many skill sets, flexibility in your approach to product and customer growth, and endurance to make sure it survives the long haul, you'll see that the smallest part (though important) is what you actually sell.
There are also so many tools out there these days that can help you quickly pick up new trends in what's selling, identify niche products within those trends, and help you identify the manufacturers of those products.
And for those who don't like selling physical products (like me!!), there are amazing platforms out there for information products and services.
You just need to shift focus to using tools to help you launch ONE small idea, and then learn how to scale that knowledge and product