They create their own measure of what "success" is. The reward for their endeavor is, at best, a sense of accomplishment at the end of an otherwise worthless life. But in real-world terms, the things that pass for actual success are looked down upon as stupid, like shoveling coal to keep a sinking ship's engine running.
Maybe, big maybe, there is a God who notices sincere effort to be a good little Witness, but that God is impressed by the qualities in a person that made it so. Honesty, kindness, etc.
Other people finish out their lives with the same sense of accomplishment, too! They have kept their dignity and integrity and loyalty to their ideals through thick and thin. At the same time they have been educated, had good careers, loved their families and kept them together, instilling good values in their kids. They may have helped with charitable movements, served others open-handedly, acted with respect toward even the poorest people.
But the Witnesses say that the heart motive disqualifies those "worldly" people and that God doesn't notice their good lives because they do it all for wrong reasons.
I'm ranting, aren't I? The arrogance of the Witnesses just blows me away.