system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Wars] if the victim knows that there /is/ such a thing as a jedi mind trick, does that diminish the efficacy of the mind trick?

What it says on the tin^

**spoilers**

It seems like the existence of the Jedi mind trick is common knowledge? At least Watto in TPM and Jabba in ROTJ are both aware of it. And Rey is seemingly aware in TFA (or else she wouldn't have known to try using it at Starkiller base).

If knowing about the trick reduces it's effectiveness then why wouldn't the Jedi keep it a secret?
gpt
It helps, sure, but not a whole lot.  
The Jedi don't keep it a secret because they can't.  Bystanders can see what's going on.  The victims themselves will later realize what happened.  
Also, it's not a technique the Jedi really like to rely on.  It's sort of a short-cut or method of last resort in most situations, so it's not worth going to great lengths to keep it optimally effective.