I believe I generally understand the concept of the (trans, not Star Trek) usage of "The Prime Directive" but as a cis person, I don't really seem to get why. If a person you know and are close to starts to act or talk in a way like they are possibly trans, why is it... not proper, for lack of a better term, to genuinely tell them "I think you might want to seriously explore these feelings"? It feels like you should? Like you should be reassuring to someone who feels like this?
Identity is very personal.
Because of how transphobic society is, one of the most universal feelings I’ve observed in people early on in gender exploration is a sort of imposter syndrome. It’s this feeling that, by claiming the label of trans or by considering that you may not be cis, you’re somehow deluding yourself or invading trans spaces. If someone has pushed you too hard to explore these feelings, it can begin to feel like they’ve somehow pressured you into changing who you are or that they’re the cause of all your repressed trauma.
There’s also the fact that repression happens for a reason. Often, the reasons for repression remain in one form or another even throughout gender exploration. Things like transphobic family and internalized sexism are common examples. Bottom line is that gender exploration is not equally safe and good for all people at all times. If someone is trans, they need to discover that in their own time when they’re ready.
What is appropriate is sharing of personal experiences. So the way that trans people often interface with The Prime Directive is to reframe those discussion and make them as pressure free as possible by focusing on their own experiences and allowing the potential egg to ask questions as needed.
This was basically it for me. When I was very young (not quite into my teens), for one reason or another, my grandmother made several remarks about how I should have been born a girl and how they should have named me [femme version of first name]. It didn't cause me to self-reflect or examine anything about my identity; rather, I felt an intense wave of revulsion and immediately shut down any possibility of ever exploring those aspects of myself that caused the remarks in the first place. It took damn near 30 years to break down those mental barriers. I'm left wondering if it would have made a difference if they'd never gone up in the first place.
Anyway, I doubt that it's a very uncommon defense mechanism for people to just shut down when someone else challenges their very sense of self. And it definitely doesn't help the impostor syndrome...