Baldessare Castiglione’s Il Cortegiano (The Book of the Courtier), first published in 1528 and translated into French in 1537, had a profound impact on European nobility during the Renaissance in all aspects of courtly life including the developing equestrian arts. As the aristocratic ideal transitioned from the medieval warrior-knight to the refined early modern courtier, Castiglione’s text served as the "golden book" that redefined the cultural and aesthetic objectives of horsemanship.

There was an expectation of equestrian excellence of the courtier. Castiglione explicitly stated that his ideal courtier was expected to be "a perfect horseman in every kind of seat" He praised the Italian aptitude for skillfully practicing the manège (complex riding exercises), especially when dealing with challenging horses. Rather than suppressing a horse's natural energy, Castiglione wrote that those who tame horses should not keep 

  them from leaping and running but should ensure they do so obediently and at the appropriate time. Training to ride and create lighter, more agile horses to their full potential thus became an integral part of courtly life across Europe.

The most significant influence Castiglione had on horsemanship was his codification of two mutually dependent qualities: grace and sprezzatura—a studied nonchalance that masks all the effort, time, and labor required to master a skill.  When looking at images of this period all noble horseman performing manege exercises demonstrate physical stillness and calm without any facial expression. Castiglione warned that the visible "exhibition of art and study... destroys the grace in everything" To be considered truly noble, a rider had to perform highly demanding and even violent equestrian maneuvers while maintaining a totally natural, spontaneous, and effortless appearance.

 The development of "Concealed Art" (Art Caché) Castiglione's philosophy directly shaped the teachings at the era's elite riding academies, largely in Italy at this time, giving rise to the aesthetic of "concealed art." Under this new courtly code, the ultimate objective for horse and rider was to hide the rider's physical aids completely. The nobleman's authority and superiority were demonstrated by making it appear as if his highly trained horse was executing complex leaps entirely of its own volition.  This standard is still with us today in many equestrian competitions.

 Because activities like manège equitation and mounted games were performed almost exclusively in public, Castiglione framed them as critical tests of a courtier's social standing. He advised that a courtier must use be strategic, using sharp judgement to determine when and where to display his skills. Castiglione warned that a rider must ensure he is flawlessly equipped and impeccably trained before engaging in any public equestrian display; if he is not ready, he should not participate at all.  To me, this was the point, prepare until the outcome is certain. Because riding was the exclusive purview of the nobility, there was no excuse for a clumsy or labored performance. A rider who showed visible exertion or lacked grace would destroy the illusion of his natural superiority, inviting brutal mockery and damaging his reputation among his peers.  How can you demonstrate your nobility, your right to rule if you can't prepare your horse properly.

https://youtu.be/ewIu07H6pDs   Here an example of the sprezzatura ideal at the Spanish Riding School