As game designer, we sell ideas to people. Sometimes we spend lots of time to make system, balance, system, UI, etc. But your boss deny it by an extremely simple sentence
It doesn’t feel good!
As my experience, most of these situations are my fault because I miss a very important part; the mechanic does not match the game theme properly. It makes my design looks stiff and unnatural
You feel everything happens naturally and comfortably in a good game. Like Star Craft, it sets in the 26th century in a distant part of the Milky Way galaxy, the game is about three species: the Terrans, human exiles and the Zerg. It is acceptable that many races live together in space. But if I design a sim game about building a metropolis, it looks silly to have many non-human creatures.
On the other hand, awkward things happened in games do not combine theme and the mechanic properly. A group of monsters suddenly come up for no reason, awkward guns sold in a cold steel background game, or creatures look completely different but live together by no reason
I think you must have faced the same situation, when you try to add some mechanics in a game feature to make it more like the real world. Sometimes they contradict, overlap or cannot connect with other logics; sometimes it’s graphically or technically hard to manage. You can’t add every idea in your mind into a GDD, the process put thoughts together is more like shape the clay into a vase. Abandon the redundant features, modify the unclear logic, add mechanic to make it more completed.
A Tower Defense game is hardly happened in a supermarket; an action game does not fit a farmland. Of course if you want to make a game different from all others, just feel free to try everything.