Human nature, that is, our natural humanity not imprisoned by the fall and its fears that give birth to passions, is inherently good. We are inclined to good, but are distracted by what is false.
The question remains: can we actually go about thinking this way?
Yes, but it is dangerous, because we often are not living according to our nature. Many of our actions are not from our true nature, but rather from the distractions we fall under.
This is why it is important at most times to remember that we are subjected for the time being to this fallenness, and must be constantly vigilant. In fact, we often must go the opposite direction from always thinking we are 'good' or 'doing good' and rather assume that everything we are doing is, to one degree or another, bad.
Sounds overly negative? Only so if you are on your own. This only works if you trust not in your goodness, but in the goodness of God. If you see that your good nature, the gifts you have and the blessing you have received, come from Him, then you can pound away on your fallenness and not lose hope. You can honestly say you have done nothing good, and it would be true: all good comes from God.
When we focus on the self, we are focusing on something unreliable. The self sometimes acts according to its nature, but other times we depart from it. However, God never departs from what is good. If we rely on Him, even our worst failures actually mean nothing, because He can and will save us.
We should not get into the business of 'forgiving ourselves' but receive the forgiveness of God. We must never assume that our own judgment is sufficient as to whether we are doing good or evil, but rather receive this confirmation from God through His servants (those who love us enough to be honest).
If you assume you are doing good, and presume that you are sufficient to pardon your own deeds, then you have no need for God. But, that also means there is no rescue when the ship hits the rocks. You'll have to swim out on your own.
If we want help, then we need to renounce our self-affirmation of our own goodness seek rather the goodness of God. We are made in His Image and Likeness, and so that goodness comes from Him anyhow. Why would you presume it is yours alone? Give credit to the One who gave it to you.
By giving glory to God, we lose the delusion of pride and selfishness that leads us to evil. We also share not only in our 'own good,' but an eternal good. A limitless good. A good that transcends all boundaries and all circumstances. Sobriety, which seems so impossible, is possible with God's love rather than our own fickle attitudes.
So, to wrap it up, it is better to see your own good as coming from God, share yourself with Him, and you can be healthy. To think you are good is the same as thinking you are bad... these are both assumptions that you can exist apart from God. This is the most unhealthy thinking there is.