Are not we dealing with the same??
The sun knows that after some time the darkness will cover him, he won't be able to spread his rays...Still he shines. Even after the darkness covers him, he does not give up. He waits for his turn and when time comes he shines again. Cause he doesn't shine for his shake only, he knows his responsibilities towards the universe as well. He knows that if he loses, the whole universe will fall in the trap of the darkness. That gives him strength not to lose hope, to fight, to shine. In Gita, lord Krishna said, "don't only live for yourself, live for others and you will be happier."
On the other side, tell me will we value sun if the darkness won't be there?? May be not. Trust me, we worship sun not because he gives us light but because of the fear of the darkness.
THAT IS HOW OUR LIFE WORKS AS WELL