This judgment is facilitated by comparing his actual history with his potential or possible history. In other words, we derive the sense of meaninglessness partly from comparing his spitting career with what he could have done and achieved had he invested the same time and efforts differently. He could have raised children, for instance. This is widely considered a more meaningful activity.
Nothing does but common agreement.
No philosopher, scientist, or publicist can rigorously defend an argument in defense of a hierarchy of meaningfulness of human actions. People often confuse Meaning and Function. When asked what is the meaning of their life they answer, using function-laden phrases. They attach different magnitudes of meaningfulness to various human activities. What they mean is really the satisfaction, even the happiness that comes with successful functioning.