Food & Drink0 min ago
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The phrase in its literal sense means that you have control over where the horse will or will not go, you have reins and can lead it to water. Once there, the choice of wether or not to drink the water is down to the horse alone - you have no control over that choice. It's used to illustrate an argument that you may have a degree of control over a situation, but somewhere along the line, there will be an element of free will over which you have no influence.