Looks, competence, workexp, interview skills, height, rich background, any positive discrimination, nepotism etc etc. All should be negatively correlated with eachother this. Although there are limits to the strength of the effect right, it depends on how much of a slice is being excluded and if the two variables have an enormous correlation that might outweigh it?
You'd also expect the effect to be stronger the more selective the environment (for each pair of variables). So if your place hires very strongly on looks and competence they'll be very negatively correlated.
Also it depends on the hiring policy, we're assuming some sort of (A+B) > C evaluation over things that they care about, but if it's (A>A0, B>B0, C>C0), pass all of those and you're in then this effect should be totally absent in those variables.
For a given car, there is no correlation between whether or not a car battery is dead or a fuel pump is broken.
However if you have a car that does not start, if you test the battery and it is working, you can now consider it more likely that the fuel pump is broken (because you have ruled out one cause of the car not starting, all other causes are now more likely).
This means that if you were to gather statistics about batteries and fuel pumps of all cars taken into the auto shop, you would find that there is a negative correlation between broken batteries and broken fuel pumps, despite this being clearly nonsensical for the general population.
If you exclude the (~a, ~b) sample then within the population that remains it looks like a and b are negatively correlated. (p(a|~b) = 1, p(a|b)=0.5)
It's interesting because this is something that happens a lot => when dating, looks negatively correlate with niceness within people you date because you don't date people who are neither. Diseases in hospital populations are negatively correlated because if you don't have anything you're not in hospital.
Can you suggest any good material you know on stats? (I'd prefer videos, but everything works)
It seems to me you have a very solid background.