One of the duties of the Knights in the medieval period was 'Shivalari' or heroism. Providing protection of women and children was the duty of knights. Thus, in front of the elite women, they knelt down and expressed reverence and love.
Besides, the knights had to take the 'Oath of Fairy', 'Oath of Fidelity', ie 'the oath of faithfulness' to the Lord. Knights have to show respect and respect while sitting on knees.
The idea comes to the boyfriend-girlfriend. The commitment to show loyalty to the people of your life is revealed by kneeling through this gesture.
He kneels in front of the nearest person and prays with a ring, only there he expresses his hopes to say 'yes', besides him also tell you that you deserve worthy honor. And modesty-love-love, this style adopted today is accepted everywhere in the world.