Different people and cultures believe different things for the answer to this question. The meaning of life as we perceive it is derived from philosophical and religious contemplation of, and scientific inquiries about existence, social ties, consciousness, and happiness.
A long-term financial plan should include these elements. Time Horizon. A plan should look at least  five to ten years into the future. Scope. A plan should consider all appropriated funds, but especially those funds that are used to account for the issues of top concern to elected officials and the community. Frequency.
But that's not the whole story. A financial sustainability plan will also include other types of resources you might obtain, such as in-kind support, volunteer staff, or shared resources from other organizations. It may even include convincing another organization to take on a project you started.