"The mortification of sin consists not in the improvement of a quiet, sedate nature. Some men have an advantage by their natural constitution so far as that they are not exposed to such violence of unruly passions and tumultuous affections as many others are. Let now these men cultivate and improve their natural frame and temper by discipline, consideration, and prudence, and they may seem to themselves and others very mortified men, when, perhaps, their hearts are a standing sink of all abominations. Some man is never so much troubled all his life, perhaps, with anger and passion, nor doth trouble others, as another is almost every day; and yet the latter hath done more to the mortification of the sin than the former. Let not such persons try their mortification by such things as their natural temper gives no life or vigour to. Let them bring themselves to self-denial, unbelief, envy, or some such spiritual sin, and they will have a better view of themselves." (John Owen – On Mortification)
Owen's point is a very good one it seems, in that we naturally tend to confuse grace that comes from nature with the grace that comes from redemption. As a friend of mine said, "If you want to seem godly, just speak very quietly." We equate the goodness we might have as a creature made in the image of God with the transformation that Christ gives us. This is very humbling and challenging at the same time. How often we take certain traits in ourselves (and in others) to be powerful signs of sanctification, when actually they are nothing of the kind. Good and valuable as they are, they are not fruit of the Spirit.
Calvin's point about us needing to repent of our righteousness, as well as our sin, in coming to Christ is instructive here. Our 'righteous deeds' need Christ as their foundation or they are not righteous. Even the virtues we have by way of common grace need to be sanctified and brought to Christ - virtues are vices unless they are "in Christ".