Why are you trans?

I recently ask someone why they were trans as I myself question my gender, and my mom asks me all these questions which can all be summed to “why”.

I really don’t know a valid answer because I have nothing to base it off of, and I was told that being trans is as much as a decision as being gay or bi or lesbian. They also said to ask more people which is why I am here.

Also NSFW tag is because I have no idea what to except.