Do bad hires happen because of (a)lack of technical/functional skills or for other reasons such as

(b)lack of the right cognitive abilities, personality, or the soft skills to get the job done or inability to fit with the team culture, the manager's working style, or organization culture?

My personal belief is that employers do a good job on (a) during pre-screening and interviews, but don't do a god job on (b).

What do you think?