You just know if you're transgender, you don't have to question it.

Someone with gender dysphoria often has difficulty expressing why they feel they should be the opposite sex. They will often simply say "it's just a feeling I have" or "I just know". This does not necessarily mean that it is innate, it just means that their true reasons are not part of their conscious mind.

Similarly, an anorexic "just knows" that she is fat. She is adamantly "insistent, consistent and persistent" in this belief. But it is obvious to everyone else that she is not.

Sometimes what one is convinced of, what one truly believes with 100% of their conscious mind, is really the mind's way of dealing with something else, something buried deep within the subconscious, something far too painful to deal with in the conscious mind.

There are many reasons why someone may identify strongly with the opposite sex. It takes time, patience and the skill of a competent therapist to uncover the true source of one's feelings and beliefs, which often lie deep within the subconscious.

So, no. You don't "just know".