It works because beliefs, desires and the like exist as real, symbol-rich, structured inner states with causal powers.
Mental processes are causal processes that involve transitions between internal representations.
For the folk psychological discourse is now imagined to track real, causally potent inner states whose contents, at least in central cases, match the contents specified by the that-clause. Chinese Room thought experiment. Searle asks us to imagine a monolingual English speaker, placed in a large room, and confronted with a pile of papers covered with apparently unintelligible shapes and squiggles. A new batch of squiggles then arrives, along with a set of instructions, in English, telling the person how to manipulate the apparently meaningless squiggles according to certain rules. But says Searle, there is no real understanding there at all.