Should the incentive of research be discussed in the literature survey? As a postgraduate engineering student, I'm doing a thesis project on a technical system that encourages people to exercise. Now I need to write a literature survey for it. As I never wrote literature survey before, I wonder whether I should discuss the incentive of my research like the advantages of doing exercises on it, which requires me to spend time looking for some sociology papers and reading them. Instead, if I just discuss the technologies used for my system in my literature survey, is it also OK?
Since you are doing a "thesis project", which seems to be a rather particular kind of writing, you should probably ask your advisor what exactly they expect of you concerning the literature review.

In general, though, normally a literature review for such a topic should mainly cover other research that is related to your topic. Specifically, I would consider surveying research on:


other technical systems that encourage people to exercise;
other systems or approaches (non-technical) that encourage people to exercise;
other research that is generally similar to what you are doing, with "similar" being fairly broadly defined.


In general, I wouldn't expect that you would need to do anything about the advantages of exercise--that is well known and understood, and extremely general. 

All that said, again, you should ask your advisor what exactly they expect.