Free will and the necessary evil

[Belacqua]

Did Aristotle make this argument based on the PSR? Or did he have other reasons for thinking this was true? 

It would be possible to believe in the PSR, and therefore there must be a reason why things fall as they do, and still misunderstand the reasons why they do so. 

Likewise Mr. Becher can believe that there must be a reason why things burn, and then posit that this reason is phlogiston. His chosen reason is wrong, but it doesn't validate or invalidate the PSR, because in fact there is a reason why things burn, whether we know it correctly or not.

If the PSR can, in some instances, lead to erroneous conclusions, how can we have confidence in it?

Can you point me to a case in which reliance on the PSR led to an erroneous conclusion? 

As I understand it, the PSR only posits that everything must have a reason for why they are that way. How we find the reason, what we conclude the reason to be, whether we are right or wrong about it, are not a result of the PSR. Even if you believe in a strict version of the PSR, it's still entirely possible to say that we don't know what the reason is, and in fact humans may never know it.