"When the builders began to remove
the drywall looking for the beam’s support (which they presumed had to be
somewhere under the drywall) they realized there was no support and the beam
fell down. The beam fell down, but not straight because it was still nailed to
all the rafters. The rafters being rigid, they don’t bend or break. If the
north and south walls had been equal, the collapse would have been symmetrical
and both walls would have pushed out as the diagonal rafters became horizontal
(horizontal being laterally longer than diagonal).