Cognitive Behavioral Therapy uses a model of human emotion which basically states that it's not the circumstances of a person's life that make them unhappy but the views they take of them. While it does, of course, admit that certain circumstances would make any sane person unhappy, it still holds true that just HOW unhappy they make a person and HOW that person will react to those circumstances will depend on a person's thoughts and beliefs.
For example, let's say your elf warrior is walking along and notices human tracks through the forrest. If he believes in the tales of legendary gold-bearing humans who come to bear tribute to any elf that they find, he'll likely react with excitement and joy. If he believes in the tales of forrest-destroying, war-mongering, and ambitious humans, his reactions are likely to be resentment and horror. The prints are the same. The person who left them is unchanged. But the elf's perspective can be very different and he will react according to that perspective.
Should the elf find the human, he could either approach according to the friendly customs of his people or attempt to frighten the human away. Let's say, the custom is to shoot an arrow into a tree near the individual to show you could have killed them, but didn't, and thus are open to peaceful talks. The human, depending on their knowledge and biases, might see it as a threat, a missed assault, a friendly greeting, a foolhardy custom, or the sign of a stupid hunter who saw him as a deer. Again, the human's reactions (and feelings) will depend on their beliefs.
This ability to interpret, reinterpret, and misinterpret events according to one's beliefs is what can be used to add so much drama into a story but, unfortunately, it can also damage the story's credibility when the beliefs are stretched to illogical lengths to justify bad reactions. The difference is the logical consistency of those beliefs. If enough contrary evidence is given, most people are willing to make an exception for an individual, even if they won't change their whole belief system. This is how you get racists who espouse racist beliefs but who are on really good terms with a local Asian or Aboriginal family.
And it does take awhile to change your core beliefs, which is something I'll go into next week.