You are an email marketing retention expert. Write a detailed, 2400-word guide on win-back email copywriting. The guide must cover: 1) Understanding why customers leave, 2) Subject line strategies, 3) Opening with empathy and value, 4) Incentive and offer strategies, 5) Urgency and scarcity, 6) Clear call-to-action, 7) Preference center and unsubscribe, 8) Personalization, 9) A/B testing win-back copy, 10) Examples of successful win-back emails.