I mean doubting could actually be realistic and maybe I should spend my time finding other ways to make money.
Doubt can be a healthy emotion. I would suggest, compare whether that doubt is a doubt of your game concept, or a doubt of your ability. If you doubt your ability, then "learn up", easily solved. If you doubt your game concept, then maybe you are onto something. Maybe your game needs an element or two that you haven't considered, and without those elements, the concept lacks. That's a healthy thought to have, and doubt may lead you to creating a better concept.
Think of games you enjoyed. Consider what made those games fun to you, down to those small elements. List them all, write them down. Then see if any of those elements fit into your game in some other form. You may find that one or more of those "fun aspects" fits, and could multiply into other related elements that bring overall fun.
Just some thoughts.