Commonplace Problem

One problem that I'm running into while writing my draft is incorporating my voice into the paper while keeping everything grammatically correct. For example, this sequence leads off my paper:

"Ah stress--we've all been at its mercy at one point or another. The night before an exam, the morning before an interview, or even gaining weight can result in some serious stress. But why? Why do we feel stressed and why do we let our stress control our lives?"

So, I know that "But why?" is a fragment, but I feel like it's necessary because it gives my paper the voice that it needs to appeal to the commonplace type of audience. Any tips or ideas as to how I could change the way this particular portion of the paper is written would be greatly appreciated!