If you are depressed, you are living in the past. If you are anxious, you are living in the future. If you are at peace, you are living in the present.

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Translated from Portuguese: Depressão é excesso de passado em nossas mentes. Ansiedade excesso de futuro. O momento presente é a chave para a cura de todos oa males mentais.

Widely misattributed to Lao Tzu. Validation can be found on Wikiquote: 
https://en.wikiquote.org/wiki/Talk:Laozi.