At one point, Rabbi Yaakov Lorberbaum (aka "The Netivot", after his commentary Netivot Hamishpat) got divorced. At the time, it was such a scandal for a prominent rabbi to get divorced that he was fired by his congregants. He was forced to make a living elsewhere and went into business. One day, he became involved in a dispute with another businessman and the matter was brought to Jewish court. The judge, who happened not to recognize the Netivot, eventually ruled against him. He then asked the judge what sources were used in the ruling. The judge replied, "Well, I mainly based myself on the comments in a quite good recently published book..." As it turned out, a book authored by none other than the Netivot himself! Yet the Netivot had completely forgotten the relevant law.
In his Pirkei Avot shiur last Shabbat, R' Herschel Shechter used this story (which he said had been recently rediscovered from old documents) to illustrate how when one has a personal stake in a matter, even a great person will find it impossible to be objective.