Our belief in the gooness of other human beings ultimately determines the success of our relationship to others. To see what I mean, I have to lay out a few basic assumptions, with which you are naturally free to disagree. :)
1. Humans are naturally good, i.e. Locke's state of nature is a more accurate vision than Hobbes'.
I won't spend too much time on this. Suffice it to say, I consider the fact that human beings are willing to cooperate at all to be positive proof that cooperation is our nature. The more advanced our society becomes, the better we get at cooperating with larger (even global) groups.
2. If something is physically possible for a human being to accomplish, then any particular human being can accomplish it if he/she does all that is required.
This one might seem a little tautological to you, but it's important. What I'm talking about is this: If you have two functional legs and a lifetime ahead of you, you can be an Olympic runner, if you put in the work. Not just you, but anyone with two functional legs.
A corollary to this is that the same holds true for personality traits. You are not stuck to your ways simply because you are a Gemini, or a Green Personality Type, or an eSTj or whatever else. Just because someone has observed something that you tend toward doesn't mean that you don't have any control over it. If you have been a pathological liar, you can make the decision to become a truth-teller any time you please. Because we are all capable of telling the truth, even a pathological liar can become a truth-teller if he is willing to actually follow-through.
3. Negative reinforcement is far less effective than positive reinforcement.
If someone behaves a certain way, and you constantly point it out, how could you ever reasonably expect them to decide to change their behavior? Undoubtedly, they will simply begin think, "Well, what's the use? If everyone thinks I'm a jerk, then why try?" Or whatever. Either the other person will start playing their negative role, or you yourself will filter out those actions that are contrary to the behavioral expectation you have set up for yoruself.
On the other hand, if you constantly and consistently reward a naughty child for any good turn he does, reward a stubborn person's occasional flexibility, reward a greedy person's rare generocity, etc., you will soon start seeing a behavioral change.
The reason for this is obvious. People enjoy doing things that benefit them. So if being good benefits them more than doing otherwise, they will learn to act in accordance with good over not-so-good.
Put it all together, and what have you got?
Really what all this comes down to is that people are good, people can change, and people will cease to do bad things if you reward their good behavior with good behavior of your own. Sounds pretty simple, but there is some philosophical optimism involved here. Why?
Well, in order to make this work, you have to have some optimisim that people who have done something bad in the past won't just keep being bad in the future, no matter what. You have to believe that being nice to people and recognizing their good deeds will make your relationship better. You have to believe that people aren't just jerks through-and-through, unless society beats it out of them.
There is optimism involved every step of the way. In order to maintain good human relationships, you have to believe that they're good relationships! You have to build that belief into your forward-looking expectations.
If you do, you'll be happy. Guaranteed.