Germany
Germans define realistic as understanding the situation as it is. And to understand the situation is to understand how it became so. Germans expect a clear explanation of the path from the past to the present. Persuasive is first explaining the history of a given situation.
United States
For Americans to be realistic means understanding what is possible. The possible is determined not only by past and present circumstances, but also by the ability to shape a new future. Persuasive is explaining how to move from the present into the future.