There cannot be two leaders in any enterprise. The man riding behind must leave it to the man in front to guide the horse. Similarly, on a tandem the man in front steers the machine and applies the brakes.
The proverb has been used as a metaphor from this practical observation and applied in various figurative senses. It emphasizes that cooperation and teamwork require proper coordination and delegation of tasks for the best results.
The proverb has been popularized through Scottish proverbs or other collections of proverbs.