An extract from The Unbearable Lightness of Being by Milan Kundera:
Yes, it was unbearable for him to stay in Zurich imagining Tereza living on her own in Prague.
But how long would he have been tortured by compassion? All his life? A year? Or a month? Or only a week?
How could he have known? How could he have gauged it?
Any schoolboy can do experiments in the physics laboratory to test various scientific hypotheses. But man, because he has only one life to live, cannot conduct experiments to test whether to follow his passion (compassion) or not.