Dec 2nd 2014, 17:23:21
It is not so much courtesy, chicken, more a matter of trying to avoid trouble.
No one likes their country to be successfully attacked and to give up land and other resources. After a single attack the player is very likely to look to see if they can attack straight back and, even if they can't, they will keep that opponent in mind and may seek revenge much later.
But two or more attacks tends to provoke a more vigorous reaction. If the person attacked cannot hit back with an SS or a PS they may well seek to get their own back by sending missiles, or tanks on Artillery Barrages or troops on guerrilla strikes or spies on any of the harmful spy missions which spies can be sent on. And having done so once they are likely to continue in the same vein.
Look in the news in any well advanced set and you will see countries exchanging these sorts of attacks. Neither is doing very much to raise their country in the scores list but they are working out the annoyance that comes from multiple hits.
Good players sometimes make multiple hits but only when they are sure the target country is so weak it will (not only now but in the future also) be unable to hit back effectively by ANY of the above ways. Much more often good players content themselves with a single grab - and try not to hit that same country again for the rest of the set.