What gave me the "right"? As a thinking, reasoning human being, I think that "right" is inherent in us all.
I rarely reject anything outright. But I do have a paradigm I'm working with.
-Technique must be useful for the environment I'm focusing on. For example, my grappling focus is on no-gi/jacketless situations. Therefor, outside of gi chokes and a few set-ups for throws, I don't really focus on gi-specific material.
-Technique must not rely on pain or "magic" to work. I'm quite familiar with a few ways to cause pain, but I'm training for an opponent who might not respond to pain alone. As for "magic", mostly I'm talking about the no-touch nonsense.
-Simple techniques are more applicable to more situations than complex ones. The more "moving parts" something has, the greater the likelihood of failure. For example, I spend a lot more time on a jab than on a spinning back kick.
-The more control I have over my own body, the better. I haven't practiced jump kicks since high school, and even though I've fallen in love with the flying scissors takedown, that and other sacrifice throws are low priority.
-Techniques must be run through the "does this do what it says" filter, taking biology and physics into consideration. For example, I've heard the practitioners of some arts say that their single, continuous-motion striking sequence (say, a hook to an elbow strike) will have as much power as the hook if it were thrown as a single shot. This violates the laws of physics.
-Techniques that have been proven to work in the environment we're training for, or in similar environments, get higher priority. For example, if a throw doesn't show up regularly in environments where throws are allowed against resisting opponents (Judo, Olympic wrestling, Sambo, Silat competitions, Shuai Jiao, San Shou, MMA, CCTV security footage) then it gets a lower priority than one that does. Hip throws should be trained more than Putar Kepala.
I think if you're an instructor, you owe it to your students to explain how, when, and why a technique works. I think if you're a student and can't make something work, even after devoting some concerted time and effort to trying, you should leave it alone, and move on to something that you KNOW works for you, and try to build a strategy around that. If you're passing on a "system", you have an obligation to teach the whole thing, but that doesn't mean you need to emphasize the parts with less-practical applications.