Tanya Chapter 30 part 3

In this exercise of humility, the thinking person considers his own struggles and compares them to those of the sinful person. The struggle that we expect of the impassioned man is the struggle that we must demand of ourselves. And we fall short, unfortunately. This is true not only in the realm of "do good," in optimal performance of mitzvos. But this is true even in the realm of "turn away from evil," completely and totally refraining from all misdeed. This being so, not only is the morally upright person EQUAL to the sinful person in his level of devotion to Hashem, but he is in fact more culpable. Because the sinful person has no understanding of the gravity of his actions, while the wise and knowing person, when he falls short -- his is a grave offense indeed.