I think the idea of primary emotions comes from the human need to feel in control. I think human feelings and emotions are too complex to classify so simply.
There are some emotions that are not really connected to any of these "primary emotions"...for example; when one feels confused...he is not sad...or angry...or disgusted...he is confused! Another example, is the feeling of disappointment; once again; I think it is quite different to any of the primary emotions.
Furthermore, not only do I not think they cannot be classified so easily; I also think that there aren't enough words in the English dictionary for human feelings...which further supports the point that they can't be categorized as such. Sometimes, I personally feel a certain way; but do not find the words to describe it;l it could be a combination of one or more emotions...that are not so easy to identify.
The topic of human emotions is one into which a lot of extensive research and study has gone in to. Psychologists have tried to comprehend how our complex and intricate system of emotion works. Classifying emotions makes it easier to feel like we have come a step closer to understanding the way that our emotions influence us. When something so complicated yet such a significant part of our daily lives; is foreign to our understanding...Fear of the unknown leads us to classify and generalize....which I personally disagree with.