So I have this raw chicken breast that I haven't opened (sealed shut in the original plastic container) in my refrigerator for 5 days now and there is still 2 days until the expiry date printed on the label. Also note that, when I bought it from the supermarket they were keeping it in a normal refrigerator, not a freezer. So my question is, if we're not supposed to keep chicken in the refrigerator for more than 2 days, how can supermarkets keep it in a refrigerator and sell it until the expiry date? 
If your chicken remained below 40F (4.5C), and in its sealed package, the expiry is valid, regardless of whose refrigerator it is in.  Any time in the danger zone (between 40 and 140F or 4.5 and 60C) reduces your window, and could reduce it dramatically depending on the temperature and time.  If you have 2 days left, and you have kept it refrigerated, I would use it or freeze it. 