It is easy to confuse such questions â `` for example to argue that people eat because they 're hungry and not to acquire nutrients â `` without realizing that the reason people experience hunger ( causation ) is because it causes them to acquire nutrients ( function ) . It is easy to confuse such questions - for example to argue that people eat because they 're hungry and not to acquire nutrients - without realizing that the reason people experience hunger ( causation ) is because it causes them to acquire nutrients ( function ) .