Sharing the Burden

I read: Rav Chaim Shmulevitz had a son born in Eretz Yisroel in the middle of the War of Independence and the bris was held in the hospital. Since bombs and debris were falling every few moments, one had to run from building to building in the short moments between bombs. As Rav Chaim was running with a relative, he spotted an injured child who was almost completely bandaged. The great rosh yeshiva  stopped running to look at the child and cry over his injuries. His relative begged the rosh yeshiva to run for cover, to no avail.

The rosh yeshiva later explained: “Foolish people think that being nosei b’ol im chaveiro (sharing your friend's burden) only means offering practical help when you can. No, the essence of this middah is to share his pain.

In case you wonder of what use is this sharing, you must know that sharing the pain diminishes it for the one who is injured” (Sefer Moach Veleiv).

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The discussion comes up now and then, whether it's a war in Israel or some other distressing circumstance, does it help anyone if I forgo dessert because other people somewhere are suffering?

I recently read that Rabbi Weitzman of Brownsville, Brooklyn issued a psak during World War II which said, if a couple wanted to marry, there was a chuppa at his house, some cake and soda, and nothing more.  No celebration, no dancing, because Jews were dying.  Rabbi Teitz of Elizabeth, NJ had a similar rule at his shul at that time.

As for this sharing the pain diminishing it for the victim, I would like to hear more about that.  How does that work? What's the source for that?