that you are kissing. You can't kiss all the people the same.
You kiss your parents out of respect and love [their boy]
You kiss your wife out of adoring and loving her [her hubby]
You kiss your kids out of your love for them [their father]
You kiss your friends out of the friendship & missing them [their friend]
You kiss the lady hand as a sign of adoring and respecting her [you are attending one old fashioned party maybe].

Well, the purposes are many but the theme is one ...
a kiss ...

Do not dwell in the past, do not dream of the future, concentrate the mind on the present moment. (Gautama Buddha)