>>you, you, your, yours

This was also the correct form for addressing a singular person who was your social superior, as in most of the other western European languages. In English, though, the use of 'thou/thee' fell completely out of favour for no apparent reason.<<

A possible reason would be that the English reputation for politeness is founded in fact? English speakers were so polite that they addressed everyone as a superior and the familiar 2nd person singular disappeared!