チョット思った。

it is an established common practice in the united states to write so-called "thank-you notes" in response to such favors as invitations to parties or gifts on various occasions.
for example, after you have been invited to and have attended a social party, you ought to write a thank-you note to the host or hostess within a few days. normally, the note should be addressed to the hostess, but nowadays addressing the note to both is quite common.
a thank-you note can be either a short letter or a card.
all you have to mention in the letter is how appreciative you are to have been invited to the party, or to have received the gift.
in case of a card, you can easily purchase a ready-made one at any supermarket or department store and add a few lines of appreciation to add a personal touch.
many Americans are introduced to this custom of writing thank-you notes quite early, almost as soon as they are able to write, in fact.
American parents train their children to respond in writing to people who have given them gifts on occasions such as Christmas or birthdays.
many children write thank-you notes even to their uncles and aunts, especially when they are unable to express their appreciation in person immediately.
most American children, with their mothers' assistance, initiate the practice of inviting their friends when they start having their birthday parties.
this occasion can be as early as their kindergarten period.
it is not an exaggeration to say that a child's first birthday party is the beginning of his or her social activities.
through birthday parties, American children are expected to learn the basic mechanisms of social activities or engagements.
they learn to invite, respond to, and behave among people in their "miniature" social gatherings.
thank-you note are considered mandatory on such occasions as receiving wedding gifts, floral gifts during hospitalization, or condolences, in addition to those occasions mentioned earlier.
in the United States, the writing of thank-you notes is a social custom that children grow up doing.
the emphasis is on timeliness and thoughtfulness, rather than proper format.
the chances are probably high that Americans write thank-you notes much more frequently than Japanese do.
the Japanese tend to write lengthy, rather formal, letters of appreciation.
thus many Japanese people end up not writing any.