The development varies greatly in length from piece to piece and from time period to time period, sometimes being relatively short compared to the exposition (e.g., the first movement of "Eine kleine Nachtmusik") and in other cases quite long and detailed (e.g., the first movement of the "Eroica" Symphony). Developments in the Classical era are typically shorter due to how much composers of that era valued symmetry, unlike the more expressive Romantic era in which development sections gain a much greater importance. However, it almost always shows a greater degree of tonal, harmonic, and rhythmic instability than the other sections. In a few cases, usually in late Classical and early Romantic concertos, the development section consists of or ends with another exposition, often in the relative minor of the tonic key.