Why is it easier to carry the same amount of water in two buckets, one in each hand rather than in a single bucket?

In both cases, you have the same amount of force in the vertical direction, but when we have a single bucket in hand there is a lot of force in the horizontal direction.
With one bucket you are constantly leaning in the other direction so that the downward force is exerting directly on your center of gravity. Holding two buckets of water in each hand does not change the center of gravity of the person.But if the person holds a bucket with the same quantity of water only in one hand, then the center of gravity moves towards the bucket (mass). Change in center of gravity causes instability of body as the gravitational force acts on it. So we feel hard to hold the bucket.