Why?

Blessed be the God and Father of our Lord Jesus Christ, the Father of mercies and God of all comfort, who comforts us in all our affliction so that we will be able to comfort those who are in any affliction with the comfort with which we ourselves are comforted by God. For just as the sufferings of Christ are ours in abundance, so also our comfort is abundant through Christ.

2 Corinthians 1:3-5 

"How would you know?  You've never been through this?"  How often has a well meaning, would-be comforter had these words flung back in their face?  Often the honest answer can be little more than an honest admission that the one offering comfort has indeed not experienced that particular trial or difficulty.  Our God longs to comfort us in our trials, as the God of all comfort.  This comfort comes through our relationship to Christ Jesus.  Our trials are an opportunity to grow in our relationship with Christ.  They enable us to comfort one another by pointing each other to Jesus with the comfort and confidence of one who found comfort in Him.