it is a difficult thing to accept when you are not being appreciated to the level of ur ability and others that are inferior or not up to your standard in terms of talent are taking all the glory. Football is not left out on this scenario , you keep wondering why some players are underrated despite their visible output on field of play, mata of chelsea comes to mind, racking numerous assists and scoring vital goals, he was simply chelsea's best player for the 2 seasons he used there but what did he get ? sold against his will to a sinking manchester united side while a certain fernando torress was left to prove himself after an extreme underwhelming two and half seasons previously at the club but they believe since he is torres, he can still come good favouring reputation over current form.
The media is a heavy determinant in underrating and overrating of football players and from my own personal perspective, i think these are some factors that are usually considered
1. physical appearance
some players are just overrated because of their height and how muscular they are while others are overrated because of their good looks i.e ballotelli, beckham, pique.
2.skills
players that are skillful tends to be overrated even if the skills are just for showboating and not necessarily translating to good stats/output on the field. townsend (tottenham) , giovinco
3.nationality
The mention of brazil as the nationality of a player makes an average football fan think the player is good, which is a big advantage to the player even without being tested . for example if an argentine and a togolese both went for d same football trial, most people will assume easily that the argentine would be picked ahead of the togolese even without both touching the ball.
and many other factors................
N.B the above players used as examples are talented but the hype surrounding them is far more than their ability.

Media also helps and the club the player plays for