Simulations are not duplications
A simulation of a fire will not burn. A simulation of metabolism in digestion will not nourish. A simulation of an automobile engine will not get anywhere. Similarly, a simulation of the understanding is not actual understanding.
The Searle argument
"The idea that computer simulations could be the real thing ought to have been suspicious in the first place because the computer isn't confined to simulating mental operations, by any means. No one supposes that computer simulations of a five-alarm fire will burn the neighborhood down or that a simulation of a rainstorm will leave us all drenched. Why on earth would anyone suppose that a computer simulation of understanding is actually understanding?...For simulation, all you need is the right input and output and a program in the middle that transforms the former into the latter. That is all the computer has for anything it does. To confuse simulation with duplication is the same mistake, whether it is pain, love, cognition, fires, or rainstorms" (Searle, 1980, p. 423).
Source: Searle, J. R. (1980) "Minds, Brains, and Programs." with peer commentary and author's response. Behavioral and Brain Sciences 3: 417-457