I never really noticed this until it was brought up today in the in-game chat, but if you view the Attunement Shard within the Forge window it will show that it can be added to Helmets;
But what it doesn’t tell you is that it’s only for specific helmets, which you’d only know if you view the shard within your Inventory like so;
Clearly this issue would also apply to Body Armour for this shard. Perhaps adding the ability to use the Alt and/or Ctrl functionality on the Shards within the Forge could alleviate this issue for people. So then they could use that to view exactly which items the shards can be used on within the Forge menu. Also, I imagine this issue applies to other shards as well (none that I know of off the top of my head).