Humans are trained from an early age to expect the happy ending. In fairy tales and literature, the good guys win, the bad guys are imprisoned (or die) at the end, and everyone lives happily ever after.
But as we grow older, we learn that evil is practically omnipresent on earth. Theft, murder, lying, and laziness are all around us, and evildoers do gain from their actions. And "karma" is a sleepy avenger.
However, even in adulthood, there is a strong human tendency to cling to the comforting illusion that good triumphs over evil on earth; that progress is inevitable, that the "tide of history" that humanity is advancing onward to a new and glorious technological paradise, free of crime, war, disease.
Of course, this is complete and utter nonsense. On earth, evil triumphs over good a lot more often then we care to acknowledge. Murderers go unsolved. Men, women, and children are brutally enslaved. Dictators rule for decades at a time, and never receive punishment. In history, the victory goes to the dark side far more often then we like to think. Those who would seek a paradise on earth are perpetually disappointed.
The 20th century is the ultimate answer to the mistaken notion that progress is inevitable. Russia and China were overthrown by Communist revolutionaries, and their people enslaved under brutal dictatorships with a callous disregard for human life. (In fairness, Russia has had a penchant for brutal dictatorship for centuries, and China's regard for human life is cheap.) Germany elected a deranged dictator and came within a whisker of conquering the world, and managed to kill millions of Jews in its death knell. The world descended into brutal and bloody world conflict on multiple occasions.
One of the advantages of belief in an all-powerful, all-good God is that at the end, there is a reckoning for our deeds. The good are rewarded, and the wicked are punished. Indeed, for Christians all those fairy tales are a reminder that there is ultimate punishment for evil and eternal reward for doing good - just not in this life. As Christians, our hope is in the Lord, not in men.
But we are not in heaven yet; we are on earth, living in this "vale of tears," and the victory of good men is by no means certain What is constant is the never-ending struggle between good and evil - one that we must fight day by day, hour by hour, moment by moment.