I explore the question of how to ground the responsibility of agents in some tricky cases involving multiple agents who act in a non-coordinated fashion. These are scenarios where no single agent has the individual ability to make a difference to a harmful outcome, but where the outcome would have been avoided if they had all acted as they should have (thus, the agents collectively made a difference to the outcome’s occurrence). I argue that an important source of the problem (...) is that it’s hard to motivate a concept of cause that can be behind the agents’ responsibility in these cases. I illustrate the problem with a particular example: Yablo’s proportionality criterion on causation. I then sketch a possible solution. (shrink)