Andrew's initial thought on his way to the patient's house is that he is thinking about the failure of marriages. This is evident from the context provided in the question.

Context:
The question states that Andrew is on his way to the patient's house. However, it does not provide any specific information about the patient or the reason for Andrew's visit. Instead, it mentions that Andrew is thinking about the failure of marriages.

Explanation:
When analyzing a character's thoughts, it is essential to consider the context and any clues provided. In this case, the question mentions that Andrew is thinking about the failure of marriages, which suggests that he is preoccupied with this topic during his journey.

1. Andrew's mindset:
- The fact that Andrew is specifically thinking about the failure of marriages indicates that it is something that has been on his mind.
- This suggests that he may have personal experiences or observations related to failed marriages.

2. Possible reasons for Andrew's thoughts:
- It could be that Andrew has witnessed the effects of failed marriages in his line of work as a healthcare professional.
- He may have seen the impact of broken relationships on his patients' health and well-being.
- Alternatively, Andrew could have personal experiences or relationships in his life that have influenced his thoughts on this subject.

3. Implications of Andrew's thoughts:
- Andrew's focus on the failure of marriages could indicate that he is contemplating the complexities and challenges of relationships.
- It may suggest that he is questioning the institution of marriage and its long-term viability.
- This could also imply a certain level of emotional or mental burden that Andrew carries, as he reflects on the difficulties faced by couples in maintaining successful marriages.

Conclusion:
Based on the given context, Andrew's initial thought on his way to the patient's house is that he is thinking about the failure of marriages. This indicates that he is preoccupied with this topic, possibly due to personal experiences or observations in his professional life.