system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't you re-freeze defrosted chicken?

Fresh chicken is fine if left out for several hours right? They usually have it sitting in the window at Deli's for hours, and then you put it in your fridge for up to a few days.

But if you freeze it, then when it defrosts, you can't refreeze it? Why can't you defrost it to fridge temperature, then refreeze it again, at least a few times (assuming the total period of time at or near fridge temperature isn't greater than the amount of time normally acceptable when unfrozen?
gpt
I've never been able to find a source that explains this clearly. The issue is not thawing in the refrigerator and refreezing, although that will somewhat degrade the quality. The problem is thawing at room temperature, which allows bacteria to grow at very high rates. 

Re-freezing does not kill the bacteria, it just stops the growth. Cooking to the proper temperature does kill the bacteria, but the higher the bacteria count the more likely is it some will survive, and in many cases the proper temperature is not reached. Cooking to 167f and holding for 10 minutes should kill all the bacteria. But that's a pretty high internal temperature and most people won't cook chicken that well.  

As for 'fresh' chicken at delis: that 'should' be kept hot if cooked and cold if uncooked. Cooked chicken is pretty safe because most of the salmonella should have be killed, so there's nothing left to grow.