As a parent and coach you are to help put the athlete in position to perform well, and that includes helping them to be in the right states of mind and emotions. During practices and previous games, the team's style of play and roles of the players should have been put in place. Pre-game talks should support what the athlete already knows and should support or help generate productive emotions. The athlete should be ready to play aggressively but under control to the right degree, and for the benefit of the team. A pre-game talk that is designed to teach new things, over analyze details, etc..., can disrupt this and be counter productive.
I encourage athletes during pregame to allow themselves to feel ready to play great, and unafraid to fulfill their roles at a very high level, because that is what the team may need! During an athlete's career, he/she needs to learn how to play great within a team concept, and within the player's character should be a humility and unselfishness that will help facilitate this. Success in sports often comes down to plays being made and plays that were not made. Not just the winning basket, touchdown, or goal, but also the hustle plays, key blocks, unselfish passes, and the like.
You want your athletes to be fundamentally sound, and in the right mental and emotional state to make plays, as well as the physical conditioning that will support making plays when fitness is challenged. Some athletes, better than others, rise to the occasion on a regular basis, and more times than not, are productive in big moments. As parents and coaches we need to be nurturers and think big picture. We want kids to compete without fear and unnecessary pressure. Making too big a deal over successes and failures can have a negative effect over what happens in the future.
Team members have a variety of needs, and are not necessarily motivated and inspired by the same things. The better the players, coaches, and parents relate to one another, the more productive the communication can be. So in conclusion, parents and coaches need to learn how best to prepare their players to do their thing on the field, and their methods of preparation need to be regularly assessed and adjusted when needed.