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When our relatives are at home, we have to think of all their good points or it would be impossible to endure them. But when they are away, we console ourselves for their absence by dwelling on their vices.
— Captain Shotover · Heartbreak House

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
Relatives at home have to be tolerated by focusing on their virtues, or living with them would be unbearable. Once they leave, the mind flips, and their faults become a comfort that softens missing them. The speaker wryly presents family affection as convenient selective memory.
Context reviewed