"On" is the social and psychological obligation taken on with favors received from others. The word comes from warrior society when lords granted to followers. It has been only 120 years since Japan got out of its feudal system. At present it is still fundamentally a vertical society, which values strict orders and strong relationships among people of different ranks.
Socially superior people often take care of their subordinates in both social and personal matters. In return, the subordinates feel "on" toward their superiors and pay them respect and royal to them.
To forget "on " is morally wrong. However, this kind of sentiment, as well as others considered to be traditional Japanese feelings, is gradually dismissing.
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