fromwikipedia

Composition
 
Brahms worked on the composition for some years, as was the case with many of his works. After a prolonged gestation period, it was first performed on January 22, 1859, in Hanover, Germany, when Brahms was just 25 years old. Five days later, at Leipzig, an unenthusiastic audience hissed at the concerto, while critics savaged it, labelling it "perfectly unorthodox, banal and horrid". In a letter to his close personal friend, the renowned violinist Joseph Joachim, Brahms stated, "I am only experimenting and feeling my way",[1] adding sadly, "all the same, the hissing was rather too much."[1]
 
Brahms originally conceived the work as his first major work for orchestra, what would have been his first symphony. After that proved unsatisfactory, he began molding it into a sonata for two pianos. He sought much advice from his friend Julius Otto Grimm.[2] However, he also found that unsatisfactory. Brahms ultimately decided that he had not sufficiently mastered the nuances of orchestral colour to sustain a symphony, and instead relied on his skills as a pianist and composer for the piano to complete the work