May you grant truth to Yaakov, kindness to Avraham, as you swore to our fathers from ancient times. (Michah 7:20)
Jewish tradition has associated Avraham, Yitzchak, and Yaakov with the qualities of chessed (kindness), gevurah (strength), and emet (truth) respectively. With Avraham this makes sense: we know from his early stories that he is extraordinarily hospitable and selfless and otherwise kind.
But it is hard to see how Yitzchak exemplifies strength, or Yaakov truth. Strength is perhaps the quality we see least from Yitzchak; he doesn't resist when his hundred-something-year-old father brings him as a sacrifice, and he refrains from purposeful action after Yaakov steals Esav's blessing. Similarly, Yaakov apparently lies to his father and deceives Lavan. How can we possibly say that he exemplifies truth?
Indeed, it's even hard to say that Avraham consistently behaves kindly. On separate occasions he expels his children - Yishmael and Keturah's sons - from his home, and he is willing to kill Yitzchak on God's command. These actions appear to reflect an extreme lack of kindness. It therefore seems that the actions of all three of the Avot contradict the attributes ascribed to them!
We are forced to say that chessed, gevurah, and emet represent not any particular deeds of the Avot, but rather their innate personality traits. Avraham, as we can see in the initial stories, possessed a powerful desire to be kind to everyone he met. We can similarly say that Yitzchak, by his constitution, was never willing to accept defeat or the triumph of evil. And Yaakov was indeed an "ish tam yoshev ohalim", who longed to tell the truth, the whole truth, and nothing but the truth.
If so, how do we explain the stories in which these qualities are not on display?
I think the answer is that the Torah does not tell us day-to-day stories of the Avot (or anyone else), but rather the most monumental and important events of their lives. Indeed, there were presumably many, many incidents in which Avraham demonstrated kindness, Yitzchak strength, and Yaakov truth. But these incidents were not the most important incidents in their lives, so the Torah does not mention most of them.
A person whose nature is kind will find it easy to perform kindness. But occasionally one is morally required to perform acts of apparent cruelty. Morality often requires that soldiers, surgeons, and politicians, for example, act in ways antithetical to the trait of kindness. A harsh or cruel person will find these deeds relatively easy, while having trouble with good deeds that require a more personal touch. For a kind person, things will be the other way round. Such is the case with every character trait, not just kindness.
For Avraham, the supremely kind person, the hardest conceivable moral challenge was to slaughter his son. For Yitzchak, whose personality would never allow him to submit to injustice, the hardest challenge was to allow himself to be slaughtered. And for Yaakov, who could never countenance falsehood, the hardest challenge was to deceive Yitzchak (or Lavan or Esav) when circumstances impelled it. In each case, the Avot's uniquely strong character traits were precisely those that had to be suppressed in order to carry out their most difficult missions.
Every person finds it easy to do good in some ways, according to the nature of their personality. But true spiritual greatness comes only when you are capable of overcoming your limitations, and do what is right even when it contradicts the inclinations of your character. This is where the Avot succeeded, and this is the ultimate goal that each of us should aspire to.
(Mostly taken from a shiur by R' Binyamin Tabory)