Speaking of players improvising cadenzas (which is what they should do), often the most agonizing ones are those inserted into Mozart concerti, which seem to have everything to do with displaying the chops of the performer and little if anything to do with the classical style in which Mozart composed, nor the themes or motifs of the piece itself. Guess there is a downside to everything…
Le Chant du Rossignol...(song of the nightingale) 