So as someone with no real knowledge of the topic, can anyone tell me what I'm missing? Our observations don't fit our models - we see an accelerating universe, rotation curves which do not meet expectations etc We decide there must be dark matter and dark energy to explain this and then try to find it. Why don't we say that our theories of gravity are wrong? I sometimes see people quoting the accelerating universe and rotation curves as being evidence for dark energy and dark matter but surely they can't be evidence when their existence is inferred from the observations in the first place! It sounds circular to me. What am I missing?