Humility and prudence.

Humility involves accurate assessment of self and one's situation. A humble person is not a lowly person, as our contemporary use of the term would suggest. We all know the image of the hunched over, pitiable creature. No, a humble person is someone who has a rationally founded sense of his own strengths and weaknesses, the features of the situation, a sound sense of what he knows about it, and where discernment is needed, how the first combines with the latter. So, a humble person is neither arrogant nor small-souled.

Prudence is the ability to recognize what ought to be done given the circumstances, and what means ought to be used. This presupposes humility, because without accurate self-knowledge and knowledge of circumstances, you cannot determine the correct course of action. You cannot even determine what the true good is that you ought to be pursuing in the first place.

Words like "cynic", "optimist", "idealist", "realist", or "pessimist" are fairly useless here. They describe willful and emotional dispositions. Sometimes, people will paint a thin veneer of "rationality" over these. They will rationalize their small-mindedness and mediocrity, or their grandiosity.

Now, you need to recognize the state of world as it is. That is not the same as recognizing how it ought to be. And the truth is that the world is a mixed bag. Each of us is a mixed bag.

Let's say the Nazis performed medical experiments on people to develop a cure (which they did). Let's say you have the disease for which that cure would work. Do you use the cure? Is it morally licit? It certainly can be (the key term here is "remote cooperation with evil"). Making use of the good effect of an evil of another's actions is not the same as committing the evil action itself. In this world, there is nothing that has not in some way benefited from an injustice. Nothing. Benefiting from these things downstream is not categorically evil. What matters are that the reasons are proportionate to the gravity of the evil, and the proximity of the act. And participating in imperfect institutions is not necessarily evil, either. It depends on what you are contributing to and how. The principle of double effect [0] is an excellent guide here.

It's not cynical to recognize that people are morally flawed. We are. We do good things and bad things, and some people are worse than others. That's just an obvious fact. But that's not an excuse to commit moral evils. That's the old defense children use: "But everyone else is doing it!" You need prudence to help you determine what you ought to pursue and how. You need prudence to be just. And you need justice to have the courage to do the right thing.

[0] https://plato.stanford.edu/entries/double-effect/