Example: Imagine that you want to write a descriptive essay about your grandfather. You've chosen to write about your grandfather's physical appearance and the way that he interacts with people. However, rather than providing a general description of these aspects, you want to convey your admiration for his strength and kindness. This is your reason for writing the descriptive essay. To achieve this, you might focus one of your paragraphs on describing the roughness of his hands, roughness resulting from the labor of his work throughout his life, but you might also describe how he would hold your hands so gently with his rough hands when having a conversation with you or when taking a walk.
It was a summer day and I was a rising senior. Despite the whipping wind driven by the A Train, the burning atmosphere still rendered me breathless in the underground train platform. I quickly stepped into the train and dropped down in a seat. I closed my eyes and rested my head on the board. Then, I immersed into inevitable sleepiness. But suddenly, my ambition to score a higher score on the SAT flickered in my mind. I rubbed the tightness on my temples and I reluctantly took out a SAT vocabulary cartoon from my school bag. Meanwhile, a group of friends who also had summer school at City College saw me and walked toward me.