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But what if you don’t feel like being happy? What if you’re just not in the mood? In His wisdom, G‑d gave us a great gift. The antidote to unhappiness is reaching out to others and helping them. Putting yourself aside, even for a few moments, in order to help someone else, provides a feeling of contentment and happiness and helps change your mindset and feelings for the better.

Lifted from Chabad.org