To be happier, what's the smallest, simplest thing an average person could do? That's the question someone asked here on Quora. People responded with a ton of good answers, including getting more sleep, focusing on the positive, shortening your commute, and exercising. But those seem like easy, tangible answers (though no less correct for it.) On the other hand, Jeff Shattuck's answer struck me as ideologically insightful, even revolutionary. He advocates "assuming positive intent."
Life's daily mishaps are easier to swallow if you assume that every offense, insult, and slight by the people you interact with is unintentional. In other words, don't take things personally. In the vast majority of cases, that person was simply trying to go about their day and take actions to make life a little more palatable for them and their loved ones. If they could have achieved the same goals without offending you, they most likely would have. There was no malice involved.
On a societal level, this goes along with what Steven Pinker has said in The Better Angels of Our Nature about the place of "honor" in societies. Honor sounds like a noble trait, until you realize that the societies that value honor above all are those in which citizens react in kind to every slight, and thus remain stuck in cycles of violence. Only by forgiving and forgetting are we able to reach peace.