How do you know that Facebook and Google have best software because of the way they do their interviews?

At their size (number of employees, number of people who want to work there) they could probably just randomly pick (or add here any other way of selecting candidates) software engineers and still get some of the best in the market that will create amazing software. Not saying this is what is happening but I am just providing an alternative explanation to underline that the conclusion hard interview => best software needs more evidence to be true.

I think the way interviews are done is a function of:

- company culture (first and foremost)

- size (how big is the company and how many people they are hiring) and churn

- their believes about building software (some people believe math is required, some people think engineering is required, some people believe no pre-requisite is required)

- employer attraction: how much/how many people want to work there

- availability/support of employed engineers to be part of interview process

- how it started (usually big companies inherit the conception about interviews from their original founders as they where the ones hiring the Cs)

- the country culture where the C level and top management is located

The problem is that soon enough, all these mediocre and wannabe companies started copying the FAANG process, thinking: "If we interview like FAANG, we must be like FAANG. Or at least candidates will think we're like FAANG." And: "If your process rejects 99 percent of all applications, then that mean we're hiring the top 1 percent."

Which is basically how the LC craze got started.

Google and Facebook are known for the best software? They are known for "some" exceptional software; but most of Google stack is crap. Facebook we can hardly know but they rely heavily on buying startups.

exactly - the proof is in the eating of the pudding.