Pronunciation is everything.
Every Spanish speaker knows how much fun it is to get their non-Spanish speaking friends to try and roll their "Rs." It's basically impossible for them and usually results in a laughing fit for everyone involved.
Like most languages, if you don't speak it, figuring out the pronunciation is hard. Words like idea are spelled and mean the exact same thing they do in English, but are pronounced differently. While others, like negar (deny), could throw some English speakers off.
The Flama , a Latino focused comedy site, got some non-Spanish speakers together and gave them various words written on index cards to try and pronounce. Needless to say the results were hilarious.
One participant thinks it isn't fair the the "Cs" in acercarse (approach, come near) are pronounced differently while another is pretty sure that ejercer (practice) means eraser. It doesn't.
Check out the video below to see just how hard Spanish really is.