Short answer: because I am a woman. Plus two more questions...
Every person’s experience is different; there isn’t a universal answer to this question. Further, there are different ways to interpret the question which can lead to vastly different answers.
The hardest part of admitting I am transgender was admitting it to myself! Telling other people was easy. Plus two more questions!
With a Tweet, J.K. Rowling has sided with trans-antagonistic and -exclusionary views. I couldn't let this go without responding. I offer this open letter to Ms. Rowling.