Historical Roots: The term originates from the battlefields of ancient China. A general's success was inseparable from the strength and endurance of his war horse. Praising the “sweating horse's contribution” was a poetic and humble way to acknowledge the immense hardship that underpinned a military victory. This reflects a cultural appreciation for loyalty, endurance, and tangible effort.
Comparison to Western Concepts: A similar English phrase is “blood, sweat, and tears.” However, there's a key difference. “Blood, sweat, and tears” focuses on the personal sacrifice and suffering of the individual. `汗马功劳` has a slightly different flavor; it often implies service to a collective or a leader. The “sweating horse” serves its master. Therefore, when you say someone has `汗马功劳`, you are often recognizing their vital contribution *to the success of a group, company, or country*. It carries a strong sense of acknowledged and respected service, not just personal struggle.
Related Values: This idiom champions the value of perseverance and tangible results. It suggests that true merit is not just about clever ideas, but about the hard, grinding work required to bring them to fruition. It is a term of high praise, often bestowed by a superior (a boss, a leader, a historian) upon a subordinate or predecessor.