In "Trains and Lovers," Alexander McCall Smith explores the fragility of one's moral standing. He emphasizes that maintaining a strong ethical foundation can be challenging, as there are numerous temptations and situations that can lead to moral compromise. People often build a perception of their integrity, but it requires constant vigilance to uphold it.

The idea that moral ground is "slippery at the edges" suggests that even minor missteps can lead to significant consequences. The quote encourages reflection on personal ethics and the potential for falling short of one's ideals, reminding readers that the journey of morality is complex and nuanced.