This idiom is very interesting and the picture is very vivid. It can be seen that it is a horse, and a fork in the road can be understood as a road. Then, combining the accumulation of daily idioms and using the method of association, we can think of "the old horse knows the way"
Old horses know their way, which is generally a compliment. It is often used to show that older people with rich work experience are easy to do a good job. Generally used as subject and predicate. For example, if we do something, experienced people will quickly identify the direction of the thing and then do it faster and better.
There is also an allusion to the old horse's understanding of maps. In 663 BC, at the request of Yan State, Qi Huangong sent troops to attack Shanrong, which invaded Yan State. The Prime Minister Guan Zhong and the doctor Peng Ji accompanied him. The army wandered around in a valley with high mountains and mountains, and finally lost its way and could never find its way back; Guan zhong had an idea: since dogs can go home far from home, old horses in the army will also have the ability to find their way. So I picked some old horses, untied the reins and let them walk freely in the front of the army. It's strange that these old horses don't hesitate to face any of them? Travel in one direction. The army followed them around and finally got out of the valley and found it? The road back to qi.