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 explaining the history of a given situation.
For Americans to be realistic means understanding what is possible. The possible is determined not only by present circumstances, but also by the ability to shape a new future. Americans expect a clear explanation of how to move forward from the present.