A long road tests a horse's strength - after ten years of working together, we finally see who is truly reliable.
Tips
history
From the anonymous Yuan-dynasty drama 《争报恩》, Act 1; the full folk saying is 路遥知马力,日久见人心. It means a long journey reveals a horse's stamina, and long acquaintance reveals a person's character.
usage
Usually only the first half 路遥知马力 is spoken, leaving the listener to supply the second half 日久见人心.