When Mozart was young a symphony was usually a short, simple piece for entertainment. Mozart made the symphony into a carefully worked-out piece lasting up to half an hour. His last three symphonies are especially fine masterpieces. His concertos, especially his piano concertos, are far more advanced than anything that had been written before. Although Mozart behaved in truly childish ways at times, he was good at understanding human character. This is clear in his operas, where he introduced many subtle effects to describe the characters in the story.