Punishment & Reward
One of the first things that came to mind when I saw the prompt was the memory of a student once asking Harisant (yoga teacher) during a yoga class why he was 'punishing' us. She was joking, but at the height of her muscular pain she meant it. Sometimes we have to hold a particular position or repeat certain movements for so long that the unused muscles start to hurt and burn so much that you don't know whether to laugh or cry or both. Harisant shouts out: "Keep up! Keep up! Only seven more minutes!"
Aaaargh! And those who have the strength or desire will 'keep up' until we break that invisible threshold and move past the pain. The reward is the moment of moving past the pain, the rush of energy and the light feeling that comes with the release, getting to lie down on the yoga mats and relax completely at the end and the sense of accomplishment of having not given in or given up.
It reminds me of life in a 'this too shall pass' kind of way. Sometimes situations may hurt and going through them feels hard. But once we 'keep up' and get past the threshold of pain, the reward is there to greet us.