The phrase "But old habits die hard" reflects the struggle individuals often face when trying to change ingrained behaviors. This suggests that despite the desire for improvement or transformation, past routines and patterns can be difficult to overcome. It highlights the conflict between the will to change and the tendency to revert to familiar practices, emphasizing the complexity of personal growth.

In J.D. Robb's book "Glory in Death," this notion is explored as characters grapple with their past while navigating new challenges. The storyline illustrates how deeply rooted habits can impact decisions and relationships, serving as a reminder that change is often a gradual process requiring both effort and self-awareness.