Real people have strengths and weaknesses. The natural human tendency is to gravitate and focus on the weaknesses to try to explain parental alienation. As the saying goes "People will question all the good things they hear about you but believe all the bad things without a second thought".
Read a Clean Example at cnn.com
The above example is a particularly clean and clear cut example, documented by the mainstream media. Because of unusual circumstances (abduction), this targeted parent has no weak points. There is clear action/reaction, with no private whispering to the child. It is simply a parent with full custody of the children and with no complaints by anyone about their behavior who then loses the children because the ex kidnaps them to another country. As always happens, the alienated children suddenly come to view their targeted parent as worthless. In this article, the targeted parent has a vague sense about the ex turning their children against him but does not yet appear to be aware that is is called parental alienation.
Here is another abduction example from the Japan times. The key thing is that everything is fine between the soon-to-be-erased parent and the child before the abduction, but then after the delays involved in processing the Hague Convention, suddenly, the child hates the erased parent.
See also: 60 Minutes exposes parental alienation , ABC 2020 Exposes Parental Alienation , Canada TV investigates parental alienation , and the BBC exposes parental alienation