diff --git a/catchup/service.go b/catchup/service.go
index de4a52a94f..ff3df36095 100644
--- a/catchup/service.go
+++ b/catchup/service.go
@@ -195,7 +195,11 @@ func (s *Service) innerFetch(r basics.Round, peer network.Peer) (blk *bookkeepin
 }
 
 // fetchAndWrite fetches a block, checks the cert, and writes it to the ledger. Cert checking and ledger writing both wait for the ledger to advance if necessary.
-// Returns false if we couldn't fetch or write (i.e., if we failed even after a given number of retries or if we were told to abort.)
+// Returns false if we should stop trying to catch up.  This may occur for several reasons:
+//  - If the context is canceled (e.g. if the node is shutting down)
+//  - If we couldn't fetch the block (e.g. if there are no peers available or we've reached the catchupRetryLimit)
+//  - If the block is already in the ledger (e.g. if agreement service has already written it)
+//  - If the retrieval of the previous block was unsuccessful
 func (s *Service) fetchAndWrite(r basics.Round, prevFetchCompleteChan chan bool, lookbackComplete chan bool, peerSelector *peerSelector) bool {
 	i := 0
 	hasLookback := false