There are two "sexes", male and female...the physical you're referring to. We historically have attributed certain behaviors and demeanors as male of female due to the general way in which females act as opposed to males, BUT, behaviors and predispositions are psychological in nature (originating in the mind) and exist on a spectrum that men and women fall on in different points for each of us. Some men and women find themselves, or purposely put themselves, in areas of the spectrum traditionally assigned to their opposite sex. Growing up we'd call these girls "tomboys" and boys would be called, "sissies" or something else. Figuring out where your behavioral traits fall on the spectrum is a part of growing up and is especially challenging in adolescent years when hormones are going crazy and are out of balance, but over 99% fall back into the general category of male and female, even if they were uncertain in these same years.
What confuses the issue is when someone exhibits psychological traits commonly held by the opposite sex to others, and is subsequently told that they are not what they were physically born as, i.e., instead of a man who exhibits "feminine" traits, you are now a "female" trapped inside a man's body and vice versa. This affirmation (wrongly asserted in my opinion) that one's position on the psychological spectrum equates to a complete change of one's position in the physical male or female standing is and has been harmful and confusing to those battling this. Perhaps the greatest error lies in assigning physical standing to psychological traits, (the exact opposite scenario) which is the historical way of determining if someone is acting "male" or "female". My solution? Separate the behavioral spectrum from the physical assignments altogether, and stop making people think that they are trapped in the opposite sex's body only to attempt a physical transformation that doesn't really work for most. Suicide and depression are just as high in post-ops as they are in pre-ops, a key indicator that physical change doesn't necessarily fix a problem that was brought on by misunderstanding a psychological one.