From Do More Better: A Practical Guide to Productivity by Tim Challies:

Your primary pursuit in productivity is not doing more things, but doing more good. Generally speaking, you can do more good for others if you have fewer roles and projects than if you have more. It is far better to dedicate lots of attention to those areas in which you are particularly talented or gifted than it is to dedicate minimal attention to the many areas you are not…

You haven’t begun to live a focused and productive life until you have said no to great opportunities that just do not fit your mission. There are many good things in this world that will go undone or that will have to be done by someone else.