Well the title pretty much says it all, I've heard our professor saying that the smallest strongly-connected components in DAG (directed acyclic graph) are its vertices. Sadly I was unable to ask him for explanation and now this is stuck in my head ever since.
This has to do with the definition of Strongly Connected Component in graph theory.
A graph to be said to be Strongly Connected if every vertex is reachable from every other vertex.
The smallest possible graph of any type consists of a single vertex. Since that vertex can reach itself (since it is itself), the graph therefore meets the criteria, and can be considered Strongly Connected.