In Robert Heinlein's 1941 short story, By His Bootstraps, the main character Bob Wilson, is afraid after searching the past and finally seeing a High One. What about this sighting invokes a feeling of sadness?
The shadow might have passed during the hours he was forced to take out for sleep. But he felt sure that he was in the right period; he kept up the vigil. He saw it. It was moving toward the Gate. When he pulled himself together he was halfway down the passageway leading away from the hall. He realized that he had been screaming. He still had an attack of the shakes. Somewhat later he forced himself to return to the hall, and, with eyes averted, enter the control booth and return the spheres to zero. He backed out hastily and left the hall for his apartment. He did not touch the controls or enter the hall for more than two years. It had not been fear of physical menace that had shaken his reason, nor the appearance of the creature-he could recall nothing of how it looked. It had been a feeling of sadness infinitely compounded which had flooded through him at the instant, a sense of tragedy, of grief insupportable and unescapable, of infinite weariness. He had been flicked with emotions many times too strong for his spiritual fiber and which he was no more fitted to experience than an oyster is to play a violin.