I'm Dutch, and people from the east of Netherland don't understand why I don't understand German, claiming the languages are so similar. But I have real trouble understanding German. Maybe when it's someone from the north-west of Germany who speaks very slowly and clearly. People from the east of Netherland have much less trouble, somehow.

(I'm utterly unable to understand people from the Dutch province of Zeeland when they're speaking to their parents. That's complete gibberish to me, though it doesn't have a special status as a local language, as far as I know. (unlike Nethersaxon, for example))