system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why is hot food supposed to be cooled before it goes into the fridge? What makes that an issue?
gpt
It's primarily a warning for restaurants.  Whatever you put in the fridge will likely cool off pretty quick.  What's most important is to not put large volumes in tall containers that will take hours to cool off.

For example, if you make a gallon or two of marinara, you don't put it right in a tall container.  You put it into several shallow hotel pans, uncovered, then, once it's cooled off, transfer to a large container.  It'll cool off super fast that way.

If you put it straight into a large container, it will still be blood warm even after cooling overnight.  That's the danger.  That's how people get sick.  Blood warm=bad.  Don't let that happen.  Hot is fine, cold is fine.

I wouldn't worry too much about the container warming up the fridge like people mention.  It'll cool down fast again.  It's all about avoiding something sitting at 95 degrees for 8 hours.  That's absolutely enough for it to spoil if there's any contamination.  As fun as salmonella is, don't poison people.