It's hard to believe nowadays, but the study of psychology for much of the twentieth century was literally delusional. The first half was dominated by behaviorism, a bad-faith philosophy of psychology - let's not stoop to calling it science - which denied the existence of internal mental states. Since virtually everyone has inner mental life, and it's trivial to design an experiment which relies on internal mental reasoning to produce outcomes, it's almost inconceivable that behaviorism lasted as long as it did; but, it nevertheless contributed a great understanding of stimulus-response relationships to our scientific knowledge. That didn't mean it wasn't wrong, and by the late twentieth century, it had been definitively refuted by cognitive architecture studies which modeled internal mental behavior in enough detail to predict what brain structures were involved with different reasoning phenomena - structures later detected in brain scans.
Cognitive science had its own limits: while researchers such as myself grew up with a very broad definition of cognition as "the processes that the brain does when acting intelligently," many earlier researchers understood the "cognitive" in "cognitive psychology" to mean "logical reasoning". Emotion was not a topic which was well understood, or even well studied, or even thought of as a topic of study: as best I can reconstruct it, the reasoning - such as it was - seems to have been that since emotions are inherently subjective - related to a single subject - then the study of emotions would also be subjective. I hope you can see that this is just foolish: there are many things that are inherently subjective, such as what an individual subject remembers, which nonetheless can be objectively studied across many individual subjects, to illuminate solid laws like the laws of recency, primacy, and anchoring.
Now, in the twenty-first century, memory, emotion and consciousness are all active areas of research, and many researchers argue that without emotions we can't reason properly at all, because we become unable to adequately weigh alternatives. But beyond the value contributed by those specific scientific findings is something more important: the general scientific understanding that our inner mental lives are real, that our feelings are important, and that our lives are generally better when we have an affective response to the things that happen to us - in short, that our emotions are what make life worth living.