If your eyes routinely hurt when doing something, and then they stop routinely hurting after you make a change, that's pretty good reason to believe that there's a causal effect there.

Sometimes the causality is clear enough that you don't need sophisticated science to figure it out. Did you know that the only randomized controlled trial on the effectiveness of parachutes at preventing injury and death when jumping out of an airplane found that there is no effect? Given that, do you believe there really is no effect?