It was the painter, and not the brush, that did the work.

“Camerarius relates a pretty little anecdote apropos of the visit of Giovanni Bellini to our artist, which he probably learnt from Dürer’s own lips. He says that Giovanni, on seeing Dürer’s works, was particularly struck with the fineness and beautiful painting of the hair in them, and asked Dürer, as a particular mark of friendship, to give him the brush wherewith he executed such marvelously fine work. Dürer offered him a number of brushes of all sorts, and told him to choose which he preferred, or, if he liked, he was welcome to take them all. Giovanni, thinking that Dürer had not understood him, again explained that he only wanted the particular brush with which he was accustomed to paint such long and fine parallel strokes; whereupon Dürer took up one of the ordinary brushes, such as he had offered to Bellini, and proceeded to paint a long and fine tress of woman’s hair, thereby convincing Bellini that it was the painter, and not the brush, that did the work. Bellini avowed afterwards that he would not have believed it possible, had he not seen it with his own eyes.” 

Albert Dürer, his life and works, vol I by Thausing, Moritz, 1838-1884