simple, 1:1 causality (if I flick a light switch, the light turns off) is not fuzzy at all. Complex causality is more complex (obviously) and most things in real life have complex causality.
In science nothing can be proven. That means in order to to prove that light switch turns the light off you must flick the switch and observe the light turning off infinite times.
If in one of these infinite observations flicking the switch off turns the light on your hypothesis is disproven. Hence disproof exists but proof is the domain of maths and logics. From this perspective 1:1 causality cannot be verified to exist.
