You know that feeling of spending years on something and not really getting it? Physics & Rendering is like that to me. Was reading this nice physics article - so many years of school & college physics summarized in one article. Pretty deep, I'm still in the Moment of Inertia thingy.. that's my moment right there.. x_x
Physics in game development is a big road block for me. For single-person / indie developers - you need to be "The Jack of All asshole" (go back and read it like John Constantine).
But the problem is - the moment you go beyond proto phase you start hitting major roadblocks in any game engine - usually graphics or physics. Either the frame rate suddenly drops and you have no clue why (I'm looking at you Unity) or Physics stuff don't work as you intend. Those times when your fucking 4 wheeler topples at 200 mph turns and you have no clue how to fix it, or things just become Kitty from X-Men.. no.. I didn't mean cute O_o