From "Chapter 6: The Embodied Brain" in The Myth of Mirror Neurons:
To say that a cognitive operation is accomplished via simulation doesn’t simplify the problem, it just hands it off to another domain of inquiry, in this case sensory and motor information processing. It’s akin to a hypothetical rogue head-of-state who calls in his top physicists and demands that they work out how to build a nuclear weapon. The physicists come back a week later and proclaim that they’ve got it all figured out:
PHYSICISTS: We have determined that Oppenheimer and his team have succeeded in building a nuclear weapon. All we need to do is simulate what they did.
HEAD-OF-STATE: Great! So how did they do it?
PHYSICISTS: We don’t know. But simulating their methods will definitely work.
MIRROR NEURON THEORISTS: We have determined that when we carry out an action of our own we understand the meaning of that action. When we observe someone else’s action, all we need to do is simulate that action in our own motor system and we will achieve understanding.
SKEPTIC: Yes, but how do we understand the meaning of our own actions in the first place?
MIRROR NEURON THEORISTS: We don’t know, but we know that simulating that process will work.