The official treatment for Gender Identity Disorder is hormones, transition and eventual surgery. The collective wisdom of learned professionals is that this is the course most likely to work. But it doesn't work for everyone. If you are 6' 10" and 400 lbs, you are never going to pass as a woman. If you can live with that, it's okay, but some people can't live with that level of rejection. If you are a fundamentalist Christian and all your friends and family are fundamentalist Christians, you've figured out by now that you have a medical condition not a sinful lifestyle - but your family isn't going to accept that. So what then?
Usually the smallest steps with which you can live comfortably are the best ones. Recreational crossdressing at home is sometimes enough for some people. Some have adjusted by wearing women's undergarments at work - but there is a certain risk of discovery and I wouldn't discount that.
What happens if nothing you try works? Maybe you've even gone "all the way" to full-time status and you are still miserable. ...Perhaps your physical size or some other feature makes it impossible for you to "pass" (i.e., be generally accepted as your chosen sex). Or perhaps you have discovered that you only thought you'd be happier as the opposite sex, but now you have found that you are just as miserable as before. What then? Are you trapped?
Persons whose drive toward changing their apparent gender stems from depression, Obsessive-Compulsive Disorder, or the internalization of rigid, false gender role stereotypes are not good candidates for transition in my opinion. Some careless therapists miss these issues, however, and people suffer as a result.
In addition to the above, there are various other reasons why a person may be unable or unwilling to transition:
It is very common for transsexuals - even postoperative ones - to have unresolved issues regarding negative gender stereotypes, as well as personal issues of self-hatred and self-absorption. These issues should be dealt with before transition is undertaken, but overeager therapists often miss or ignore these vital issues. The trend over the last several years has been to offer only ONE solution to the complex and multifaceted problems of gender dysphoria and Gender Identity Disorder.
Some people may feel that they have already gone too far and can't turn back even if they are miserable. However, I've met a few people who've gone back to their birth gender, one was post-op. Nobody seems to keep statistics on "failed" transitions, and even if they did they probably wouldn't count all the suicides. Whatever your situation, however, I want you to know that there is hope. Transition, hormones and surgery are the best solution for some but not all persons suffering from gender dysphoria. Nobody chooses Gender Identity Disorder but we do make choices in what we do with it. Sometimes only one choice will actually work for you but sometimes you can find alternatives. You might choose instead to seek treatment for some underlying causes of gender dysphoria: Negative birth-sex role modeling, false glorification of the non-birth gender, cyclic depression, and/or obsessive-compulsive disorder.