Light Bulb just went on. How magic works? (Newbie)

[Zen]

You can't stack the same items to create effects.

The only instance where you can is a creature with 4 Misc slots (like an Oracle) and you have to place one item in the first and second slots and another of the same item in the 3rd and 4th, if you don't place it that way you won't get the benefit.

You can however, in the case of a natarajah, equip both types staffs of elemental mastery because they're considered different items.