A chess player's attitude probably has as much to do with winning and improving their chess game than anything else. A chess player can spend months reading books, practicing games, and memorizing openings, but if that chess player does not posses the winning attitude he or she will only advance so far in his or her abilities.
I am not going to suggest that you need to be an overly joyous soul to be good at chess, but you do need to work on some attitudinal skills such as confidence, respect, determination, discipline, etc. All of these traits can help make you a better chess player and perhaps a better person. Confidence in your game and your skills does not equal an arrogant person, confidence means that you know you are an intelligent person with some chess skills who could beat anyone on a given day. Confidence means that you are approaching the game with an attitude that you can in fact win the game at hand if you play well.
Respect for other players is important as well since you do not want to take an opponent so lightly that you do not try your best when you play. Determination means that you are willing to put in the practice and time that it takes to become a great chess player. If you look towards grand masters as people you would like to emulate, then understand that they got to where they are by practicing, studying, and learning from their mistakes.
Finally discipline is needed to have a winning attitude. The discipline to critically think through your moves, the discipline to sit and analyze the games that you have played, and the discipline to analyze the games of the chess greats is needed to develop a winning attitude. Disciplining yourself into good study habits will definitely help improve your game and your attitude.