In a windmill, doing one’s work is highly dependant upon the weather. If there hasn’t been a wind for weeks and work is building up, would one be tempted to engage the machinery, even if there was some risk of a storm.
Windmills would regularly be destroyed through just this process: the mill would get out of control, braking systems would fail and the machinery would be destroyed or, sparking, would ignite the suspended dust of the milling process, causing an explosion.
A windmill is a powerful piece of machinery, "built like a tank", and the miller’s job is an important one. If he’s temped to engage the power of the machinery unwisely, even with the best of intentions, disaster can result.
Turndust narrates the scenario above as an extended metaphor for the implementation of power in general.
Interesting fact: wheat was first developed for agricultural use in Mesopotamia.