"Frustration" is a great exercise to develop your arc-like shape phrases and make the music more expressive with this fundamental technique. It features a sad and gloomy atmosphere with a "molto ritardando" (translates to slowing down considerably) at the end of the piece. Out of all the pieces in this collection, only three are based on folk tunes: numbers three, six, and eight. The rest of the pieces were created in their entirety by Bartók using folk-like structures and melodies.