In any endeavor involving multiple parties it is important for people to understand their roles and responsibilities toward the ultimate goal. Teams that have worked together for a long time can easily fall into well developed patterns of responsibility that can change quickly and fluidly based on situations. Newer teams need more up-front definition to make sure responsibility is always handled.
Across the many, many projects I have worked on the most consistent reason for failure was failures of responsibility. Either someone was put in charge that didn’t want to be or didn’t know what to do or no one was put in charge with no one stepping up. Leadership doesn’t always require a “leader.” Sometimes all that is necessary is someone to accept responsibility (which is many people’s definition of leader).
If you have any question of who is in charge then it is likely everyone else does as well. The person in charge often makes it clear by setting expectations. Lack of expectations is a sign of no one taking responsibility.
To be successful, first understand your roles and take responsibility for them. Don’t deflect blame, accept it. Don’t brace for failure before you start. Own your world.