Aristotle says that pleasure and pain are of vital importance in the education of the young. We reward children for good behavior and punish them for bad behavior. This is how they learn virtue.
In the case of an adult, however, such positive and negative reinforcement should no longer be needed. A virtuous man is one who takes pleasure in acting virtuously. This is the link between virtue and happiness, which Aristotle calls the ultimate good.
Aristotle views virtue (at least in adults) as a disposition rather than a way of acting, giving no credit to those who act virtuously but find the experience painful. A brave man will derive pleasure from facing danger, whereas a coward will find it painful. Always to find virtuous actions pleasurable and vicious acts painful is the mark of an excellent character.