People don’t notice whether it’s winter or summer when they’re happy.

The line suggests that genuine happiness absorbs attention so fully that external conditions—symbolized by the seasons—lose their power to register as important. Winter and summer stand for hardship and ease, gloom and brightness, or simply the passage of time; in a state of contentment, these contrasts blur because the mind is not preoccupied with discomfort, waiting, or lack. Read this way, the remark is less about meteorology than about perception: happiness alters what we notice and what we deem worth noticing. It also implies a quiet critique of lives dominated by dissatisfaction, in which every change of circumstance is felt sharply because inner well-being is absent.