As long as you believe that you are separate from others, you cannot really know them. In order to know people, you have to sense that they live within you.
In this way there is a link between you that allows you to sense what they are experiencing.
Sometimes you have no idea that the person next to you is suffering, because there is no communication between you.
But look at a mother: she can sense that her child is suffering even when they are far apart, because there is constant communication between them.
You must build your lives on the idea of unity. When this idea has become the basis of your relationships with others, everything will become clearer; you will understand others better.
You may even become clairvoyant.