The quote from Ian McEwan's novel "Sweet Tooth" suggests that daylight represents clarity and rationality. It implies that the light of day brings out the truth and straightforwardness of situations, much like how common sense operates in our lives. When we think of daylight, we often associate it with visibility, understanding, and transparency, which can parallel our ability to make sensible decisions.

This connection highlights the contrast between obscurity and enlightenment. Just as sunlight illuminates the environment, common sense guides our judgments, making them more reliable. McEwan may be exploring themes of perception and understanding, emphasizing how clarity in thought mirrors the brightness of day, offering insight and wisdom in a complex world.