Although we are social beings, being social in itself is quite hard. Luckily enough, we manage to pick up a few tricks through our experiences. Take for instance the way we understand the behaviours of others. How do we make sense of it in our head? If you invite someone over for lunch and they decline, what do you conclude? They don't like you? They're busy that same day?
They don't want to seem "too available"? Psychology calls this study as Attribution. Under it, we study how we make judgements about people's actions.
Jones & Davis' Correspondent Inference Theory
One way is given by Jones & Davis, who proposed that we make judgements about people's personalities and traits on the basis of their behaviour. However, it is not as simple as it looks because all forms of behaviour may not be reliable sources of judging someone's personality. Take for instance a waitress at a restaurant. She is paid to do her job and may hence be friendly, polite and proactive to the customers. However, it would be questionable to conclude that this is her actual personality as there is an external factor (possibility of losing her job) controlling her behaviour. Her actions are not freely chosen. Hence, we focus on actions that are free and voluntarily made.
We also focus on actions that lead to consequences that could not be caused by anything else. In other words, unique consequences. For example, if you meet your friend's fiancee and discover that she is attractive, but dull, boring, and incompatible with your friend, you would conclude that he is marrying her for her looks. But if she had a more interesting personality, you would not be able to conclude much.
Lastly, according to Jones & Davis, we look at actions low in social desirability more than normal actions. In other words, actions which are out-of-the-ordinary. If you meet someone at a party who is polite, would you make any special judgement about them? Probably not. But if you meet someone, and they're being unnecessarily rude, you would probably make an evaluation about them. This is because we cannot really conclude much about a person just because they follow social norms, but we can conclude at least a bit more about a person who goes against such norms.
Harold Kelley's Causal Attribution Theory
There is another theory by Harold Kelley who proposed that we attribute others' behaviour to either internal or external causes on the basis of certain information. Internal causes are those that come from within i.e. one's personality, motives, intentions, health etc., while external causes are situational and imposed. The information we look at are consensus, consistency and distinctiveness. Take the example of a student who scores an A grade in his English assignment.
Consensus is the extent to which others react the same way to the situation. Do other students also score an A grade? If yes, then you can conclude that consensus is high. If he is an exception, then consensus is low.
Consistency is the extent to which he responds the same way to the same situation across time. Does he always score an A in his English assignments?
Distinctiveness is the extent to which he responds the same way to other situations. Does he score an A in other subjects like say History or Psychology?
If consensus and distinctiveness are low, but consistency is high, we can conclude that the student really likes English or is gifted in English since he always scores an A. But if consistency and distinctiveness are low while consensus is high, we can conclude that he probably just got lucky or that the paper was easy since so many students scored an A. If consistency and distinctiveness are both high, then regardless of consensus being high or low, we can conclude that the behaviour is internal. Perhaps, the student is by nature hard-working.
Of course, these processes are far from conscious—they all operate so subtly that only when learning and articulating it can we be surprised at our own complex instantaneous judgements.