A lesson about eyeshadow primer

The other day I was engaged in a heated debate about the virtues of eye shadow primer. A friend of mine insists that it is a silly idea for silly people with too much money and time on their hands. I whole heartedly disagree. She reckons eye shadow is fine on its own. My oily eyelids and collection of cheap and cheerful shadows say otherwise. In the end I pulled out some Urban Decay Eyeshadow Primer Potion and one of the worst quality shadows I have (A matte purple MUA one). Behold:

Can you guess which swatch has the primer? One little tube of loveliness transforms a sad little pot of shadow which barely shows up and disappears on me within a couple of hours into a gorgeous vibrant purple that lasts all day. I win x