Hello, all this talk about gravity and what exactly this is really interests me, but I don't seem to be able to understand exactly what about it is that is the hard part to solve, there seem to be so many factors involved that I'm losing track of the entire picture. So, could you tell me what exactly a good theory of gravity should be able to describe or explain? Mainly which experimental results it should explain, and which theoretic constructs that follow from other experimental results it should be compatible with. Also, could you tell me what the main theory's about gravity say, where they fall short, and why they can or can't be combined if applicable. Perhaps a list like that could help me and other curious but not too knowledgeable people understand what the problem is about. If anyone could help with that then it would also be of great help if statements about it could be put in not too technical terms that also avoid formulas as much as possible, it's not going to help much in my understanding otherwise at least (but if it can't be put in a way a 5 year old would understand then the proper explanation would be great of course). Thank you for your time.