well i can cast fire using my staff wand, there dosent seem to be any mechanic on how thats even possible, we simply call it magic.
Same thing with the shield, it would be considered magic, enchantment or infusion, w/e they like to call it.

Much like myself, im an artist i can paint, design etc...idk why i can do this & many others cant, i just can...
Some claim... it's in your blood, some say its a gift... and some say genetics, to me it dosent matter much, i just accept it as it is.

I hope this made some sense to ppl. ^^