Originally a comment by Sastra on Imprisonment by dogma.

Having a “trans child” in the family is like having a psychic child, a reincarnated child, a child with Multiple Personality Disorder, or a child who’s been to Heaven and returned to tell us about it. If you’re in a milieu which values their acceptance or which insists that it’s important to always believe and support your children, then a child’s insistence, sincerity, and suffering will be considered good evidence. You were skeptical, but swayed. You listened. You checked things out thoroughly from all sides, your evaluations are fair and your recollections reliable. So are theirs.

Being close gives you an advantage. Having “skin in the game” gives you authority. So does love. Your child’s improvement and smiles mean you must be on the right track. Their tears when they’re rejected or thwarted rightly stirs your protective instincts. Having a loved one or friend who’s trans is supposed to give someone better insight for judging whether the trans-identified are experiencing what they say they’re experiencing for the reasons they say they are.

It’s actually the opposite, if we’re really trying to get to the truth.