Salesforce Flow: What is going on in there!?
Salesforce's Visual Workflow and Process Builder are incredibly powerful tools but can be very difficult to troubleshoot. I struggled to make these tools effective until I was able to get a glimpse of what was happening inside. Salesforce has some suggestions for how to troubleshoot failing flows but often these tools provide incomplete answers. Particularly for auto launched flows, these techniques are often insufficient.
Answering why this failed doesn't have to be a rabbit hole.
Debug log to the rescue!