Instead of coming up with idea and guessing what would be useful, I did research on problems people had, and then got additional evidence that a particular problem I'd discovered resonated. (See e.g. https://stackingthebricks.com/how-do-you-create-a-product-pe... for intro this approach.)
That meant every time I had those negative thoughts, I could come back with "but you have so much evidence!".
(In my case evidence was: bunch of online discussions of people talking about problems, wrote some blog posts about those problems, one blog post got tens of thousands of hits, and other blog posts on topic got lots of hits too. So clearly a problem people have. And product is something these particular people will pay for.)
If they don’t burden your life, think them through. Is it true? Would nobody use your product? Would you? Ask someone else if they would.
Another good thing to start with is the why. Why are you making the product? Are you trying to become rich? Are you filling a need? Are you doing it because it’s fun? Are you learning something?
Everyone fails though, what matters is that you admit it when you do.
Knowing when you’ve failed can be a bit tricky though, especially when you haven’t made an exact mistake. So set some goals for your product, and evaluate how you meet those goals, and if you don’t, evaluate if it’s worth setting new goals or trying something else.
The fact that I didn't get something right the first time doesn't mean that I will never be right. With each attempt, you learn something new. Thomas Edison made 1000 unsuccessful attempts at inventing the lightbulb, but learned, adapted, and tried again. If you learned something, you didn't fail :)
Go for it.