Many students are challenged but the requirement to use or even develop theory in their dissertation work. Those who come from a practical background may regard theory with skepticism, and see little value in working with it. However, stripped to the basics, all theories are just structured discussions of belief about how different phenomena fit and work together.
Most doctoral programs require you to review and integrate theory, or perhaps several theories, into your research. Hypotheses are usually based in theory, and developing a good explanation of how theory is relevant to your dissertation focus or topic is usually very useful in understanding the problem, and choosing a method and design to research the problem.
One of the common problems I see in dissertation proposals is a discussion of theory, but little alignment between the theory discussed and the research questions or design that is proposed. A failure to demonstrate how theory connects to your questions, hypotheses, and design can slow you down in getting your proposal accepted.
We have posted several relevant resources about working with theory in various sections of this website. In particular, you may find the following resources helpful: