We must make the best of those things that are in our power, and take the rest as nature gives it. —EPICTETUS, DISCOURSES, I.1
In matrix organization, you may not get the power because no one reports to you. However, to get everyone on the same page, we need to keep reminding ourselves on the ultimate outcome.
The more projects I attend to the more I understand that project management is not just WBS or PErT or Microsoft project. It is the dealings of people to create the outcome we wanted. If things are not in my power to do so, look for someone with power to do so.