Tolstoy: Anna Karenina

Now, though his conviction that jealousy was a shameful feeling and that one ought to feel confidence, had not broken down, he felt that he was standing face to face with something illogical and irrational, and did not know what was to be done. Alexey Alexandrovitch was standing face to face with life, with the possibility of his wife's loving someone other than himself, and this seemed to him very irrational and incomprehensible because it was life itself. All his life Alexey Alexandrovitch had lived and worked in official spheres, having to do with the reflection of life. And every time he had stumbled against life itself he had shrunk away from it. Now he experienced a feeling akin to that of a man who, while calmly crossing a precipice by a bridge, should suddenly discover that the bridge is broken, and that there is a chasm below. That chasm was life itself, the bridge that artificial life in which Alexey Alexandrovitch had lived. For the first time the question presented itself to him of the possibility of his wife's loving someone else, and he was horrified at it.