Answer:
Often the reason* for transvestism is the cross dressing of a boy in childhood by a female relative mixed with envy of girls. In my own case my sister dressed me in her clothes from aged 3 years. I envied her greatly because she was a stronger and more confident person than me. The most influencial part of the cross dressing experience in childhood involves enjoyment. As a child my mother was a cold and unloving woman; except when my sister cross dressed me. She found this hilarious and took photos of me with ribbons in my hair wearing my sisters dresses. Thus I was encouraged to cross dress because when dressed as a girl I was loved and told by my mother that I should have been a girl, was as pretty as a girl and looked good in dresses. If these remarks are reinforced for many childhood years then when a boy reaches adult hood he associates cross dressing with love and pleasure.
As a teenager I became addicted to wearing my sisters clothes when she was out. At puberty I found wearing girls clothes sexually exciting and began crossdressing to masturbate. All my sexual fantasies involved being crossdressed by a powerful woman and taunted by being made to perform feminine roles. For instance the idea of being made to wear a french maids outfit and to clean a house at the direction of a dominant woman is a common trasvestite fantasy. Most fantasy indulged in by transvestites involves forced to become female type scenarios. I believe this fantasy is a mechanism for overcoming the shame of crossdressing by the scenario of being forced into dressing by a more powerful woman.
It is not necessary that the boy experiences being dressed as a girl for transvestism to result. The above writer touched on the more fundamental cause when he wrote 'As a child my mother was a cold and unloving woman...'
When a young boy (<7 years of age) loses his natural mother and is then brought up by a stepmother, he not only experiences a profound bereavement; he is often not loved by the stepmother. The loss of the natural mother and lack of comfort offered by the stepmother can result an emotionally fragile child, who weeps easily. If she fails to understand the child's behaviour, belittling him with phrases such as 'you should have been a girl', criticising and generally finding fault, the child is ripe for the cue which will probably occur at the onset of puberty.
The original writer's fantasy about being crossdressed by a powerful woman and taunted (often) by being made to perform feminine roles is universal among transvestites and persists throughout life, even though the mature (and experienced) transvestite will develop more sophisticated techniques for acting out his female fantasy, with extremely convincing makeup, wigs and choice of clothes.