Oh man, it's a constant struggle. The implementation is always more complex and seems to take longer than first anticipated.
I would say personal expectations matters a lot. I tend to play out big visions in my mental theater in a very conceptual sense, then get hyped up with excitement and finally get disappointed every time I hit a brick because it feels like taking several steps back.
But again this is about personal expectations/attitude towards these discoveries. Objectively, it is a good thing you have found a flaw/difficulty/problem. They are a natural thing in the development process.
I have learned, through experience, to take it calmer and understand that even simple concepts might hide complicated implementation details and take time to get done properly.