Damson trees are brittle; it's an unfortunate distinguishing characteristic of this fruit tree.
You could have a bough that’s loaded with damsons and then, in an instant, and for no obvious reason, the bough shears away from the ‘mother trunk’.
A load of your crop is lost and your tree is denuded.
The wound caused may open the tree to disease.
This short video shows the aftermath of such damson tree brittleness. It captures a large bough that had a good crop of damsons on it that now lies on the ground after splitting from the tree.
Lots of fruit lost, for sure.
Tempremental trees? Probably.
What can you do to preempt their brittle nature? One suggestion is to prune judiciously so boughs don’t get so heavy with fruit that they break.