I once (a couple decades ago) built a rear wheel and was plagued by broken spokes. After three or so, I finally took a close at the bend (on a spare spoke from the set) and found that instead of a nice radiused curve at the elbow, there was a sharp bend. That sharp bend would concentrate the stresses at that point and result in a spoke breaking . In other words, I had purchased a bad set of spokes. No one could have built a reliable wheel with those. I do not recall the brand, but it was one of the well know names in spokes.
Once I found that, I removed all the spokes and started all over rebuilding the wheel set -- and, checking the spokes before I installed them.
Mike