The main reason why a team becomes unsuccessful is due to the ineffective leadership style of David kind of leaders who fail to motivate their team members to produce high-quality outcomes. Additionally, impossible goals and moral problems are also significant reasons for project team failure. Impossible goals can lead to demotivation among team members, while moral issues such as frustration and dissatisfaction with roles and responsibilities can cause performance problems. It is crucial to prioritize team member satisfaction to ensure the success of a project.