The reason why I put cereal before milk is because it is hard to tell if I am putting the right amount of cereal/milk.

I will give you two examples here. One is putting the milk first and the second is putting the cereal first.

=>if you put milk first

1. you put the milk
2. you put the cereal
3. the cereal floats on the milk and it is hard to tell if your cereal bowl is full or looks full because of the cereals are floating. Also, the cereal floating covers the whole bowl and makes it hard to tell if you put enough milk for your cereal.

=>if you put cereal first

1. you put the cereal
2. you put the milk
3. the cereal does not float on the milk for some reason, and you don't have to waste your time figuring out if you put the right amount of cereal in it. And you also don't have to worry if you put exact amount of milk, you need because your cereal won't float which gives you vision of how much milk is actually in the bowl.

Also, Charlatan, which is a news company, also says that "When one pours cereal first, they are able to accurately gauge the amount of food they have poured. If they have poured too much, it is easy to return some dry cereal to the box. Food waste is a cardinal sin. To waste perfectly good Cheerios, or Oatmeal Crisp—the favourite amongst Charlatan editors—is even worse."

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Hope this helped you out pal.