diff --git a/examples/preferential-optimization/evaluator.py b/examples/preferential-optimization/evaluator.py
index 355af4d7..ee1950c5 100644
--- a/examples/preferential-optimization/evaluator.py
+++ b/examples/preferential-optimization/evaluator.py
@@ -85,6 +85,7 @@ def main() -> NoReturn:
             continue
 
     if len(comparison_trials) < n_comparison:
+        # Wait for unfinished trials (images under generation) to be generated.
         time.sleep(0.1)
         st.experimental_rerun()