Sine qua non

Sine qua non is a fancy way of saying something that is absolutely necessary for something else to happen or work. Let's pretend you are making a cake. Flour is the sine qua non of making a cake, because without flour, you cannot make a cake. Just like how you need special ingredients to make a cake, some things are sine qua non for other things to happen. It's like a puzzle where all the pieces have to fit together perfectly. Without each piece, the puzzle is incomplete and won't work.