Are Community Rituals Organic or Intentionally Created?

Rituals always come up organically, or can they be intentionally created by a community organizer? It is always better to build on something that's there organic. Look for the things that people already doing. How do we celebrate anniversaries? How do we say good bye when some one leaves? Or do we create a slide show where we honor all that person's contributions and tow the story of times when that they were massively influential for us?