I can only imagine, but my understanding has been that some people can feel neither inherently male or female and regularly move between feeling like the two, or in other instances, may not feel like either, at all.
It's something I don't think a person will ever understand without experiencing it to some degree, and as it makes absolutely no difference to my life whatsoever if someone identifies as one particular gender, two genders, or neither, I'm more than happy for them to live their lives as they feel is appropriate for them. Additionally, if there are things that can be changed to make their lives easier, or to make them feel more comfortable in public settings, such as changing announcements from starting, "ladies and gentlemen," I'm more than happy for these changes to be made.