"Good manners are the technique of expressing consideration for the feelings of others" (Alice Duer Miller).
SHOWING CONSIDERATION FOR OTHERS IS EASIER WHEN WE HAVE SOME PRECEDENTS TO FOLLOW. If, for example, someone did us a favor and we had never in our lifetime seen or heard anyone else respond considerately to a favor being done, we might have trouble figuring out how to respond appropriately ourselves. In such a situation, it's a big help to know that saying "thank you" has been proven over a long period of time to be a considerate response. Being able to fall back on a useful precedent is a great relief. So in the final analysis, that's what good manners are: ways of "expressing consideration for the feelings of others" that time has proven to be valuable.
Mannerliness amounts to making others as comfortable as possible in our presence. But making others comfortable requires that we be comfortable within ourselves, and so Alexander Pope wrote, "True politeness consists in being easy one's self, and in making everyone about one as easy as one can." True mannerliness is always an outgrowth of personal integrity, principled behavior, and peace of mind.
Most worthwhile things take learning and practice, and mannerliness is no exception. If, as Alice Duer Miller writes, good manners are the technique of expressing consideration, that technique needs to be acquired. Good intentions are not enough -- we have to learn what are the time-tested ways of showing our good intentions.
Going to the trouble to learn and practice mannerly ways is one way to say "I love you" to those around us. Especially when we're in a country or a culture different from our own, it takes extra effort to find out how consideration can best be shown in that environment, but making that extra effort is how we show that we truly care.
In a busy world, we need to make sure that things like good manners don't become casualties of our busyness. In fact, it can be argued that the busier and more stressed out we are, the more we need to be mannerly. The "technique of expressing consideration for the feelings of others" is a skill that we should never be too busy to use.
"Life is not so short but that there is always time for courtesy" (Ralph Waldo Emerson).