Spot on and absolutely paramount: if you cannot appreciate what you have, it feels like you don't even have it. So you could be rich and still feel like a pauper - it's that subjective.
Regarding "That Skinny Mom At Preschool Pickup", most likely she has issue about her body image anyway. I never ever met a woman who was 100% satisfied with her looks.
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"Gratitude unlocks the fullness of life. It turns what we have into enough, and more. It turns denial into acceptance, chaos to order, confusion to clarity. It can turn a meal into a feast, a house into a home, a stranger into a friend. Gratitude makes sense of our past, brings peace for today, and creates a vision for tomorrow."
(Melody Beattie)