Want to be happy? Don't make this mistake

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Across
  1. 1. rest
  2. 4. come back
  3. 7. harmful
  4. 8. error
  5. 9. flourish
  6. 10. concentrate
Down
  1. 2. surroundings
  2. 3. joy
  3. 5. ultimately
  4. 6. issues