“What caused the problem that interrupted the process, and who will do what to resolve it?” 

Creating a Lean Culture, 3rd Edition by David Mann (CRC Press, 2015) p. 112.

Note from Ray: The Lean approach is to build this cycle into daily work:
1) DETECT problems as they occur
2) SELECT the important problems to work on
3) CORRECT problems by turning them into action-assignments:
Who will do What by When to resolve the problem?