There are no objective metrics nor particular reasons in life in general. It's an ad-hoc mesh of people interaction. Some consider it a game. People choose their friends and put them on some scale of close friends vs. acquaintances based on how much they like them and how well they connect with them. From an individual's perspective, people are never equal or the same: people are nice and interesting wildly unequally.
The same works for employers, employees, and co-owners: they want people with whom they can connect enough so that they can work with them. If you do connect with a person, you end up hanging out with him/her, and this opens the door for creativity and new ideas and projects.
Conversely, nobody wants to spend time with people they don't particularly like or connect with, even if they are highly skilled. Interviews are always very personal in the end, even if people want to back up their choices with seemingly rational and objective analysis. That's why there's an array of diplomatic answers to why the candidate was rejected. But basically it often comes down to "I didn't get a good feeling of him", and that hunch is likely to be correct in most cases (I'd personally venture to say "in all cases") but you're not allowed to say it aloud.
In life you don't win by getting the numbers right: you win by letting go of too much idealism, seeing instead what works 1) for real and 2) for you, and then by hopping on to the right carriages while journeying on.