5 whys is my go-to debugging strategy for truly mysterious software and systems bugs. The rubber hits the road at the point where you have an answer like "one

5 whys is my go-to debugging strategy for truly mysterious software and systems bugs. The rubber hits the road at the point where you have an answer like "one of A, B, or C occurred" and you don't know which because none of them are ever supposed to happen :) you know you're within a clue-bat-swing-radius of the problem then.