Attitude is just as important as performance. Young players make the mistake of not making this a priority in the early years of their career. It can literally be the difference between having a 10+ year playing career or being let go after preseason in their rookie year. I've seen countless times over the course of my career, young players come into a club with a selfish mentality of thinking everything is about them and clubs should appreciate it they are a part of the team. Sadly, this same mentality, poor attitude, is the cause of being cut from the team.
Like anything in life, people want to be surrounded by those with a positive mindset that bring the environment around them up instead of tearing it down. Remember soccer is a team sport that relies on team moral to get the organization through tough games and situations. When a player arrives to a new team and he or she has a poor attitude it makes the clubs job very easy in getting rid of the cancer.
Talent will only take you so far. I believe that talent alone won't get you the results you are looking for on any team you play on. Talent can help you get out of tight situations on the field or make a player visually appealing to the untrained eye. The competition level is incredibly high and the game is so complexed that talent alone won't be enough. Having the right attitude and staying humble will get you farther and I am a testament to that in my career. Clubs and teammates want a player that is honest and puts in the hard work consistently. Every. Day. I realized this very early in my career and kept that in my character everywhere I played. If their was only one piece of advice I could give any young ambition player it would be to have a positive attitude and remember your attitude affects the environment around you.