Bad designers never doubt their work.

Onur Cobanli explica:
Most designers love their work as they love their children, everyone does it; but if you love your child, you want your child to be in a better wellbeing; that can be due to internal and external conditions; external is where you live, the society, the environment and ecosystem, and internal is how you treat your child and about your child development; such as skills, languages, hobbies and quality times you spend with your child; now, most designers love their work as they love their child, and most therefore fails to see how their amazing child could be more amazing, keep your eyes open; invest your time and effort to see what can be better; maybe you need to spend more time playing, maybe you need to hire a private teacher; likewise for your design you may need more iterations or you may need to consult an expert or you may need to do more research; have a healthy amount of doubt about your work, that's the only way to be a better designer.