I have some issues with understanding exactly how the arrays and memory works in solidity, but I found this nice question that kind of help me to understand some parts - Solidity 2D in-memory array with size defined by a variable
I see how the 2D array can be initialized, but why we have to mention the exact size for the first dimension (X axis)?
In my case, I know precisely how big the array can be, so it is fine, but what if I do not know how many elements I can have on X axis?