There are two types of fairness, lets call them Macro and Micro - it's easier to talk about unfairness than fairness as it's generally only when something is unfair that people complain.
Micro unfairness typically comes to the fore in a situation where both parties start at situation A, both have equal opportunities and make the same decisions but one party profits, sometimes to the detriment of the other party and usually due to external factors. The party that did not benefit from this situation will deem it unfair - however the party that did will argue that given equal opportunities were available to both parties the situation was entirely fair.
Macro unfairness is illustrated by a situational benefit that one cannot change - ie. you are born into royalty, no matter what I do, or how suitable for the job I may be I will never be King of England.
Something is deemed unfair if it impedes a persons progress to a goal which they think they are deserving of. Whether it is unfair is actually inconsequential - in this way "fairness" and "luck" have a lot in common. Ie. you may have a terrible car crash and survive. It is lucky you survived, it is unlucky your car is written off. Depending on the importance you place on both these factors will influence whether you perceive the event as a lucky or unlucky event.
