It was one of those perfect English autumnal days which occur more frequently in memory than in life.

The line contrasts lived experience with the mind’s selective, idealizing recall. A “perfect English autumnal day” evokes a culturally loaded pastoral ideal—clear light, crisp air, mellow color—yet the speaker immediately undercuts it by noting such days are “more frequent in memory than in life.” The effect is both atmospheric and quietly skeptical: nostalgia edits out inconvenience, and the past becomes a curated gallery of “perfect” moments. In a crime novelist’s hands, the sentence can also function as tonal misdirection, setting a serene surface against which human unease or violence may later register more sharply.