The pilars are important. But in software testing manytimes the requirements are interdependent. They are related to eachother.
I've thought about a schematic respresentation.
This is what I've came up with:
But wait. That's probably not the way you'd like to build your software, right?
So, where do you start testing?
Many times I see people work hard, but they are not focused on the most important things. Selling a product 999x is nice, but would you like to sell a product which is wobbly and doesn't meet the requirements?, of course not!
Well, with this in mind you might want to read the great Twitter post of a highly appreciated expert in the field :
In essence: of course you want to test the most important requirements, the lowest pilars hypothetical spoken in this case. But in order to be sure all the base requirements are tested well... you must have a sharp eye on a couple of important things.
Remember in software testing,
paradoxes always lurk!