Final answer:
Castiglione believed a courtier should behave with strict etiquette and manners, exude grace, and not everyone should behave like courtiers but can benefit from some aspects of courtly behavior.
Step-by-step explanation:
According to Castiglione, a courtier should behave with adherence to strict etiquette and manners. The concept of grace is essential to courtier behavior, which is an effortless elegance combined with excellence in both arts and arms. It involves being well-versed in the scholarly and physical activities expected of a nobleman at the time. One achieves grace through practice and natural talent, but also by appearing to do these activities effortlessly.
Castiglione's ideal courtier should be assertive but not dominating, able to understand and manipulate situations subtly, much like the tactics described in the references provided (64-68). They suggest a strategic approach to interactions which closely aligns with being tactful and diplomatic, qualities Castiglione valued in courtiers.
According to Castiglione, not all people should behave like courtiers as this behavior is specific to those within the courtly environment. However, elements of grace and good manners can be beneficial in varied social contexts.