In an ideal world the careers we pursue would be guided by our strengths, our aptitude would determine our success and we would be rewarded with merit for how good we are at doing our jobs. This concept is known as meritocracy and it's usually primarily in the context of governments, namely those which claim to appoint people to their key positions based on ability and proven track records. If you've paid attention to politics in recent years even briefly so, then you will know this claim is patently untrue. This isn't a political post though, much as there is to say on the matter I would mostly be echoing what you've already heard a thousand times over.
What interests me about the idea of meritocracy is its application beyond government to everyone else and the jobs that they do. Judgement of politicians to one side, they are not the only people we see in jobs and feel they're in the wrong profession. The truth is that capitalism doesn't reward ability it rewards durability - or permanence. The people who remain in their jobs are those that can withstand the pressure of their job, even if they're crap at it.