Hard on himself and easy on others. That is, what others do, regardless of how much Torah and how many Mitzvot [commandments], he understands that others did not have the same understanding that he does. Hence, whatever they do is good because he is easy on them and everything that others do is fine in his eyes.
However, he is hard on himself. That is, everything he does, he sees that it is not alright because his intention while doing the good deeds is not the real intention. For this reason, he always sees that others are better than him because their actions are fine, and about his, he thinks the opposite. At that time, he can make an honest prayer about his situation, that he is in such lowliness.