You have two genders: biological and psychological. When a child is born, there can be a hormone imbalance which will assign the wrong psychological gender. For example, if I was trans (which I'm not), I'd feel like a female trapped in a males body. The worst fear of mine would be puberty because it causes irreversible changes to the body. Therefore, t's best to transition as early as possible to make sure those changes don't happen and I can be happy. Remember that a hormone imbalance IS NOT a mental illness. It doesn't cause any negative side-effects. The only reason why trans people commit suicide is because they aren't accepted. They are ostracized and bullied. 1 in 12 trans people are murdered in the U.S and between 49-60% of them attempt suicide. The entire LGBT rights fight is akin to the civil rights movement in every way. To answer your last question, some just don't want the surgery but want to use hormonal therapy instead. Some use both.