The team mentality is something that all team members should have. No team member should be either self-absorbed or intimidated by the team's individual roles, and team members need to be open to working with one another for a common goal. In order for a team to succeed, everyone must think of themselves as part of the team and contribute in the best way possible. This is especially true in team sports, but it can apply to any team activity that requires cooperation between two or more people in order to accomplish a larger objective.
The key to developing a team mentality is communication and trust. If you don't communicate your ideas when you feel they are necessary, how will other team members know they can count on you? It's also important to build trust. If team members don't trust one another, they may not want to open up and share their ideas. Team mentality is important because it can help team members resolve conflicts and avoid team dysfunction. When team members work together with a unified front, they will be able to focus on the team's goal rather than on individual problems that might arise along the way.
Having team mentality also means working as hard as you can and never giving up. This applies both in real life and in team sports: if a team has more than half of its players thinking of themselves as individuals rather than part of a cohesive unit, they won't succeed very often. Having team mentality means training yourself to think about your team first instead of yourself first; this creates an environment where team members support one another and work together to accomplish their team goal.
This team mentality doesn't just mean thinking of your team as the entity that is doing something; it also means thinking about how you can benefit your team. For example, if you are at bat in baseball and there are runners on first and third base, the hitter has an obligation to sacrifice himself for his team by putting himself out so that someone else - either the runner on third or the runner on first - gets a chance to score. This isn't all players' responsibility, but everyone should at least think about what they can do to benefit their team before themselves. If you can put yourself out for your team but choose not to because it might make you look good, team mentality isn't something that you possess.
This team mentality also means keeping your eye on the team's goal at all times. If you forget what team you are playing for or why you are doing this in the first place, it might be time to reevaluate what team mentality means to you and how much of it you really have.
As always, remember that developing team mentality can help make any team activity more fun - whether it's a team sport, a board game with friends or family members, or anything else involving collaboration between multiple people.