"It is more difficult than you think."
Translation:È più difficile di quanto pensi.
I'm no expert so just putting my two cents in here.. We know that "quanto" translates like "quantity"="how many". So to me, the way I read it is "It is more difficult than how [much] difficult you think it is". I don't know if that helps or makes it more confusing. I always try to translate it back to English to see how they construct sentences and help me remember how to say certain things.