I really shouldn't jump on your thread but I have a quick question!!!

I got confused whilst in Spain about UK > Spanish adapters.
If you plug your UK 3pin socket into an adapter, you can put the adapter into the wall either way round, as its just 2pins.
How does this work?!
Doesn't that mean that you could be connecting positive to negative, or positive to positive depending on which way you plug it in??!

I'm sure there was nothing to stop me turning it around, yet I cant see how this works.

Sorry for butting in but I couldnt find anything on google