Many people fear leftovers, but they shouldn't if they are properly refrigerated and not left out for 3 weeks, when bacteria can grow. Unfortunately, not everyone follows food safety rules. They eat petri dishes of leftovers and wonder why their stomachs hurt so badly.
You can only leave meat and cheese at room temperature for a limited time before they become unsafe to eat. A pepperoni pizza can sit on a counter for two hours before it starts to look a bit suspect, but that won't stop a lot of people from eating it anyway. Who among us can say that we've never eaten some food that has been left out longer than it's supposed to be?
One of the greatest Reddit posts of all time is about someone eating pizza left out on the counter overnight. A young man saw a pie like that on the kitchen counter when he woke up and assumed his roommate had forgotten to put it in the refrigerator. He ate a slice, and then his roommate was infuriated to discover that he had eaten a slice of the pizza. Apparently, it was the roommate's birthday, and every year on his birthday, he ate a whole pizza that had been sitting at room temperature for hours because that is how he liked to eat it. He accused his roommate of ruining his special "birthday pizza." You would think the reasonable people of Reddit would either find this absurd or understand why this guy wouldn't assume his roommate was planning to eat this unsafe-to-consume pizza. If you thought that, you would be wrong! Literally every comment criticized this guy for eating his roommate's special "birthday pizza" and condemned him for eating somebody else's food. You would think he was doing his roommate a favor by eating the food-poisoning pizza!
In reality, neither of those guys should've eaten that pizza, but pizza is one of those foods people feel more comfortable taking risks with when it comes to food safety. I don't think that guy would've eagerly drank a warm glass of milk that had been sitting on the counter all night. Meat, especially chicken, is also much more suspect after too much time. That's why the son in this story is horrified by his dad leaving a milky, cheesy pasta dish with chicken at room temperature for 24 hours before eating more of it.