Rav Shmuel Vosner ztz"l once visited a yeshiva boy who became very ill. The boy endured severe pain on a daily basis, but he displayed so much strength in spite of it. He was always pleasant and smiling. When asked how he was able to be so strong, in spite of what he was going through, he replied, “I have often thought about what my purpose in this world is. Why would Hashem leave me here to live like this? It then struck me, the Gemara says that the Shechina rests upon the head of sick individuals. If so, one of my purposes with this illness is to bring down Hashem’s Presence into the world. That is how I am able to serve Him. Isn’t that a very important job? I also realized, there’s another Gemara that says the Shechina cannot reside in a place of sadness. Therefore, I try with all my might to veer away from sadness and depression. That is why I am always smiling, because that is the way I do my job and bring Hashem’s Presence into the world.”