“Diffusion of responsibility is a social phenomenon which tends to occur in groups of people above a certain critical size when responsibility is not explicitly assigned.”
http://en.wikipedia.org/wiki/Diffusion_of_responsibility
This can be a problem in large meetings or discussion forums. Issues are identified, and action might even be suggested. Unless someone specifically takes ownership for an action, everyone might assume someone else is doing it.

directly responsible individual « snippets of cloud said
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