Jesus identified mourning as a blessing because when we mourn the death of our loved one, God will make sure we are comforted. God uses fellow believers as comforters to those who are mourning.
We have all had, or need to have, difficult conversations. An email that offended or troubled us, a blow-up at a family dinner, a situation at work that is unbearable, a church feud that is spilling out into the community or friction within a house