Are we rational or irrational?

It seems as though there is a conflict in world of economics. As an economist in the making I have been taught that for economic models to be effective we must first make assumptions about what we are attempting to model. Constantly I have been reading or watching or listening about information on economics and most of the time they start with talking about the assumption of rationality (or irrationality). It seems entirely unclear as to whether the economic community believes that humans are rational thinkers and actors or if they are irrational. I think it changes from time to time, and from subject to subject. It seems the more I research the more I find that the 20th century was full of assumptions of irrationality, but that is the only time when such assumptions were widespread. Even now, not even a decade later than that time period it seems that we have moved back into the realm of assuming people act rationally. What is to the cause of such changes? I certainly have no definitive answer, I'm not that well versed in economics... yet. If I had to give it a guess I would say it has to do with the political climate and the perceived ability of humans to do the right thing. It could also be linked with whether people are acting selfishly (a sign of rationality) or as a whole the society in question is acting selflessly (a sign of irrationality). This bring into question how do we measure the true selfishness/selflessness of a persons actions. Tangent aside, I suppose the whole rationality debate is based on opinion and the only way to find the solution is to make models (possibly with both assumed) and see if they hold up.