Diagnosing problems in deployed distributed applications continues to grow more challenging. A significant reason is the extreme mismatch between the powerful abstractions developers have available to build increasingly complex distributed applications versus the simple ones engineers have available to diagnose problems in them. To help, we present a novel abstraction, the workflow motif, instantiations of which represent characteristics of frequently-repeating patterns within and among request executions. We argue that workflow motifs will benefit many diagnosis tasks, formally define them, and use this definition to identify which frequent-subgraph-mining algorithms are good starting points for mining workflow motifs. We conclude by using an early version of workflow motifs to suggest performance-optimization points in HDFS.