The relationship between reason and the emotions is one that has been wondered about for a very long time--going back to our most ancient literature, including the Old Testament and Homer's Iliad. I doubt that I will be able to resolve this one for you, but I do have a suggestion to make.

I'm not sure this is a philosophical question, but I also think that you (or most people) can do what you say you can't do. If you think that you are feeling a certain emotion that is not compatible with a rational assessment of things--for example, you feel as if you are falling in love with some movie star whom you will not likely ever meet--then there are various rational steps you can take to get rid of the emotion. Ever heard the one about taking a cold shower?

OK, maybe it is not as simple as that, but we certainly can look for things that will divert our attention from an emotion, or will use the energies of the emotion in different ways (and thus serving to deflect it, as part of a strategy of extirpating it altogether). Simply reminding ourselves of the irrationality of some feelings we may have will help us to get rid of them (or transform them into something else). There can also be rational strategies for getting help--if an emotion is especially troublesome, it is rational to seek assistance from professionals who can work with you on why you may be feeling some things that seem very irrational to you. Understanding the source of an emotion is also a potent tool for restoring us to a reasonable life.