Bobby the mountain climber was famous for his attempts to climb the big snowy mountain. He had tried it at least thirty times, but had always failed. He began the ascent at a good pace, focussing on the snowy summit, imagining the marvellous view and the sense of freedom up there. But as he went on, and his strength dwindled, his gaze would lower, and more often would he look at his worn out boots. Finally, when the clouds had gathered round him, and he understood that he wouldn't be able to enjoy the view from the summit that day, he would sit down to rest, relieved to be able to start the descent back down to the village, though slightly worried about all the jokes he would have to endure. On one of these occasions he went up the mountain accompanied by old peeper, the town optician, who bore witness to the failure. It was peeper who most encouraged bobby to try again, and he presented him with a pair of special sunglasses. "If it starts clouding over, put these glasses on, or if your feet start hurting put them on too. these are special glasses; they'll help you."Bobby accepted the gift without giving it much mind, but when his feet started hurting again he remembered what peeper had said, and he put on the glasses. The pain was pretty bad, but with those new sunglasses he could still manage to see the snow-covered summit; so on he continued. Just as nearly always seemed to happen, misfortune returned in the form of cloud cover. But this time it was so light that he could still see the summit through the clouds. And so bobby kept climbing, leaving the clouds behind, forgetting his pain, and finally arriving at the summit. It was certainly worth it. His feeling of triumph was incomparable; almost as magnificent as that wonderful view, resplendent in its silence, the mountain below surrounded by a dense sea of clouds. Bobby didn't remember the clouds being as thick as that, so he looked more closely at the sunglasses, and understood everything. Peeper had engraved a light image on the lenses, in the form of the snow-covered summit. It was made in such a way that you could only see it if you looked upwards. Peeper had understood that whenever bobby lost sight of his objective, he would similarly lose sight of his dream, and his will to continue would wane. Bobby realised that the only obstacle to reaching the summit had been his own discouragement. When he could no longer see the top of the mountain, the problems had set in. He thanked peeper for using that little trick to help him see that his aims were not impossible, and that they were still there, where they had always been. 
If we lose sight of our main aims we can often abandon things when the first difficulties arise. 