diff --git a/sandbox/tx_handler.go b/sandbox/tx_handler.go
index a6048bf94ebd574aee5f8a954a0779bfdd1d8d5e..58323b43f9cd3e43e6e520abc1b9b8b78ff00b0b 100644
--- a/sandbox/tx_handler.go
+++ b/sandbox/tx_handler.go
@@ -195,6 +195,12 @@ func (h *TxHandler) handleTxRequest(msg *protogo.DockerVMMessage) error {
 		txResponse.Events = responseEvents
 
 	} else {
+		// If tx failed, we don't need to return wset and rset:
+		// - wset: wset is always dropped for fail
+		// - rset: rset can not be dropped for fail
+		//  - from simContext: simContext already has such keys, value is not important
+		//  - from wset: simContext don't have such keys, but it will not cause conflict for applying simContext,
+		//               because even if other txs are written first, the read set here will eventually be dropped
 		txResponse.Code = protogo.DockerVMCode_FAIL
 		txResponse.Result = []byte(response.Message)
 		txResponse.Message = "Fail"