Rashi explains that Eliezer had a daughter whom he would have liked to see married to Yitzchak Avinu. Thus, he had a vested interest in the success or failure of his mission. Failure meant that Yitzchak might become his son-in-law. This could create pressure on even the most objective mind. The commentators wonder why, specifically at this point, when the shidduch has been successfully concluded, that Rashi mentions Eliezer’s personal negios, vested interests, rather than doing so earlier, when Avraham Avinu had originally sent him on the mission. The accepted explanation rendered by the Rishonim is that Eliezer was well aware that, being from Canaan, he was considered an arur, cursed, and an arur cannot marry with Avraham Avinu’s seed, who is a baruch, blessed. It was after Lavan referred to Eliezer as a baruch, that Eliezer felt that he could possibly enter into matrimony with Avraham.
The Kotzker Rebbe, zl, offers a powerful insight. As long as Eliezer had a vested interest, he did not realize that his decision was impaired by his personal agenda. We are blinded by our special concerns to the point that we believe that we are acting in good faith, all the while unaware that everything we do is impugned by our personal stake in the matter. Eliezer was influenced by his own interests, thus unable to discern that he would have been quite pleased if Rivkah’s family would have refused the match. Only later did he sense his misgivings, because he was no longer nogea b’davar, no longer had a vested interest in the outcome.