What are they and why?
Please discuss here...
The responsibility of being the only son in the family is a socially induced phenomenon. (im going to post my own opinions now without even doing any research so if anybody would care to correct me or back me up, i welcome it)
Since the time when mankind discovered that the sperm that comes from men will impregnate the woman who has the egg, it has been thought that a family's "line" will be carried on by the male. This ideology is not only present in oriental civilizations but in western civilizations as well.
The responsibility of the male in a family was to spread his seed and therefore his family line so that the family will grow "stronger". As numerical superiority was seen as the most basic measure of strength, the more descendents in a family tree, the stronger a family is. Such responsibilites are extended to the security and the well being of this "family" which probably gave rise to how many societies place breadwinning responsibilites on the males.
In present day, such "responsibilities" are slowly diminishing in both western and oriental but comparatively, it is still more prevalant in oriental ones. The more traditional generation prefers to have a boy in the next line of descendents not only to keep the family line going, but to keep the family "strong". Many rituals in oriental customs still place importance on the eldest male in the family, the most notable of all being chinese funerals.
Thus being the only "son" in the family carries all the burden that could have been shared by brothers that he doesn't have.