Final answer:
The nurse should respond in a supportive and empathetic manner, acknowledging the client's feelings but also providing reassurance and encouragement for their recovery journey.
Step-by-step explanation:
The nurse should respond to the client in a supportive and empathetic manner. One possible response could be: "I understand that you're feeling discouraged right now, but it's important to remember that recovery is a journey with ups and downs. Many people have been in your shoes and have successfully overcome addiction. You have the strength to kick this habit as well, and we will support you every step of the way."