Why it is so important for Business to handle Cultural Differences effecttively?

Since Western investors came to Poland, Western managers and Poles are working together in many companies. How effective this cooperation is? And how effectively Westerners and Poles are cooperating when they start a business project? Besides of the large numbers of existing financial, legal and administrative problems which are to be solved here as a matter of "hard facts", the issue of intercultural cooperation is of high importance, too. If this cooperation which belongs to the "soft facts" does not proceed very well, the loss of invested energy, time and ...