How to not block yourself when planning new features?

So I've been a professional software developer for about 5 years now. What I have learned is that even "small" features tend to become very deep, and I catch myself getting lost in thought blocking myself from being able to confidently implement new features. I still do it though, as it's my job. But the "what if" never leaves my head, and I am never confident about my solutions. As an example, whenever I implement a new feature, after having a rough idea