"The heart knows its own bitterness, And a stranger does not share its joy."
Even when we've experienced sorrow in our own lives, we can't perfectly sympathize with another person. Each human -- each heart -- has its own hurt. We can come alongside, but we can't see inside another's heart. And what is true for sorrow is also true for joy. The fullness of one person's joy is still singular to them. It can't be completely comprehended by another. "We all need sympathy. And as it is impossible that we should ever perfectly obtain it from our fellow men, there remains but One who can give it to us. There is One who can enter the closet where the skeleton is locked up. One who is in touch with our unmentionable grief. He weighs and measures that which is too heavy for us to bear. That blessed One! Oh, that we may each one have Him for our Friend! Without Him we shall lack the great necessity of a happy life! A personal Savior is absolutely needful to each of us to meet our individual personality. Jesus, alone, can understand with our joy and make it still more gladsome. He, alone, can understand our grief and remove its wormwood." (Spurgeon)