Under what conditions is collaboration not possible?
None. Collaboration doesn’t rely on conscious or willing partners. A blind or unaware melding of disparate elements still results in a – albeit dysfunctional – collaboration.
Hannah Arendt recalled her friend and novelist Mary McCarthy in this way: ‘It’s not that we think so much alike, but that we do this ‘thinking business’ for and with each other’. Shortly before dying, Arendt realized that she was not going to be able to finish editing her last book, The Life of the Mind. She asked McCarthy to finish it for her. How does “thinking alike” and “thinking together” feed collaboration?
I don’t think ‘thinking alike’ is necessarily beneficial, sparks fly and things happen when opposing forces meet, as long as a functioning coalition can be maintained for a period.
When we look at a forest, the first thing we see are the trees, individually striving to reach the light.  What we don’t see is the massive mychorrhizal network underneath our feet.  While fungal networks cannot produce their own food, they are nonetheless responsible for distributing resources and information throughout the forest: they are the mediators that help the other plants to work together.  What and/or who mediates collaboration, and what are its effects on the process?
Everyone that comes into contact with the collaboration has a stake in its outcome, from the viewer to the gallery or event organiser. And by having a stake in the outcome they become a part of the collaboration.
Draw a visual diagram of a collaboration you did for a certain project.
Visual interpretation of Sluice__ as an organism:
“Haeckel Siphonophorae 7” by Ernst Haeckel – Kunstformen der Natur (1904), plate 7: Siphonophorae (see here, here and here). Licensed under Public domain via Wikimedia Commons – link.