Free choice / discretion

Hello Rabbi,
I understand that you believe in free choice, meaning that humans can (not always) exercise discretion to choose how to act.
But what does the concept of "judgment" mean? According to what you write in your books, it is some kind of spiritual entity that receives input from our brain and senses and makes its own assessment and causes our body to act in a certain way.
It sounds like that entity is also bound by the laws of causality. If it receives inputs from the brain and determines the output accordingly, then it is deterministic. If it is possible for the same input to give different results, then it is random and there is no discretion here.
In fact, the concept of discretion by definition is deterministic, because I weight the inputs to output using the data I have (a strictly deterministic process).
The question is, how is the concept of discretion actually non-causal (=non-deterministic)?