Generate a full detail guide on the practice of gratitude. The guide should be uplifting and practical. It must include sections on: 1. The Science Behind How Gratitude Affects the Brain. 2. Different Ways to Practice Gratitude (e.g., a gratitude journal, gratitude jar). 3. A Step-by-Step Guide to Starting a Gratitude Journal Habit. 4. How to Practice Gratitude Even on Difficult Days. Please include a disclaimer that this is a wellness practice.