Keep your thoughts positive because your thoughts become your words.
Keep your words positive because your words become your behavior.
Keep your behavior positive because your behavior becomes your habits.
Keep your habits positive because your habits become your values.
Keep your values positive because your values become your destiny.

Mohandas Gandhi (1869-1948) Indian philosopher and nationalist [Mahatma Gandhi]

(Attributed)

Never specifically cited, and attributed with variations in the language. Also attributed as a Chinese or Buddhist proverb.