I've had this general idea floating around in my head for a while as to why dwarves get strange moods.
There is a magical world that is home to the ideas for every artifact that could ever exist. Under normal circumstances, this world cannot interact in any way with the material one. However, since it is formed from pure thought and tied to creation, the plane can be brought closer to our own with thoughts of art and creativity. These thoughts are most common in the industry-obsessed dwarves (Armok knows they don’t think much about anything else). In an area with a sufficiently dense population of dwarves, the barrier wears so thin that occasionally an idea can cross over into the material plane. The artifacts of the plane of ideas desire nothing more than to be created, and exist exactly as they were meant to. When one crosses over, it will find a suitable host with a preference for dwarves whose former work runs in a similar vein to their own form. They inhabit the mind of this dwarf, inspiring him or her with a vision of their own perfection, usually convincing that dwarf that the idea was the product of their own imagination. Dwarves again prizing and obsessing over art and industry, they will become completely consumed by the quest to create the item they have seen. Once the requisite materials have been gathered, the idea itself guides the craftsdwarf’s hands as they conjure it forth from mundane materials. While the dwarf is not truly in control as they believe they are during this process, their mind is able to reverse-engineer, at least to the degree it is possible, how one could go about designing such an incredible object. Thus, when the artifact is complete, the dwarf in question will have an understanding of their field beyond that of even dwarves who have spent their entire lives working to master the same skills the old-fashioned way. If another artifact idea makes it through, it will avoid those dwarves who have already been taken as a conduit before, because their minds will be subtly geared to understand true perfection only in the context of their first artifact, which could lead to flaws in the form of any subsequent artifact creations. Such flaws go unnoticed in lesser objects because the knowledge of perfection grants an advantage far larger than the disadvantage of misapplying that knowledge for dissimilar items. Occasionally, rather than taking the subtle approach, an idea will simply steal control of a dwarf and displace their normal mind. This will create an artifact in the same manner, but the dwarf will not learn mastery of their craft from such an event, and it leaves them able to recognize and reflexively reject any new idea that tries to take them. Also, occasionally the dark mood a of a fortress will most strongly attract artifact ideas for evil, morbid designs. No matter what mood is taken, the dwarf will deliberately forget if they ever truly understood that they were not the originator of the idea that they helped to realize, for it is a far happier thing to be the brilliant master artisan who created such a wonderful thing than to merely be the slave of a being that even still, despite being better qualified than any of their peers, they cannot hope to understand. Dwarven society doesn’t look too closely at what is really going on, because both the artifacts themselves and the dwarves that have made them are resources far too precious to be concerned about the source of.
Any thoughts from anyone else?