First principles thinking is a very helpful mental model popularized by Elon Musk.
First principles is the idea of breaking down a problem into its most fundamental and simplest parts.
For example, if I wanted to create the best chicken parmesan sandwich then I would want to break this down into what the most fundamental parts of a chicken parm roll are.
In other words, I want to know what the most basic ingredients are - bread, cheese, tomato sauce and chicken.
I would then go about getting the best bread, the best chicken, the best sauce and the best cheese before I even think about what oven to use or what temperature to cook it at because the type of oven and the temperature of the oven are useless if I don’t have the right ingredients.
I can then think even further and try to be more creative to create the best tasting chicken parm roll.
For example, everyone uses mozzarella cheese but is that the best tasting cheese? Perhaps brie cheese might be a better ingredient to think about using when making the best chicken parm roll since brie cheese is a more richer tasting cheese than mozzarella.
If cost is a factor then I would probably not use brie cheese and would go about looking for the best mozzarella cheese.
An example of first principles thinking being used in the real world is when Elon Musk solved a problem he had of getting a rocket at an affordable price for what would eventually become his space company, Space X.
He noticed that it was very expensive to buy a rocket so he broke a rocket down to its most fundamental parts which consisted mostly of raw materials like aluminum, titanium and copper.
He then set out to make an affordable rocket by buying the raw materials on his own and then using them to assemble a rocket from scratch.
It worked and he was able to create an affordable rocket to launch into space.