predictive coding minimises the costs needed as the brain needs only to transmit the deviation compared to the raw signal. Think of vision, nearby pixels are similar (part of the same object), so by using predictive coding you only code the changes between neighbouring pixels. that reduces the amount of information that needs to be transmitted a lot! from experience the brain sets up what to predict, has been shown in the visual system to be within seconds) but it is not a fortune teller, it is rather a comparison between expected = predicted and experienced = real (sensory) input. If your model (prediction) is quite accurate, you get no error signal. No updating. No learning.