In any Directed Graph, like DFA or NFA, If we wish to find All the Reachable nodes(states) from some node(starting state) then we can just apply Breadth First Traversal or Depth First Traversal on that DFA or NFA from Starting State.
The Idea is that Some State $Q$ is said to be Reachable in any DFA or NFA Iff there is Some Path/walk from Starting state to that state $Q$.
Since, Every Walk contains a Path. We can simply remove Walk from above theorem.
@Mohit The full address was definitely on the ...