K'Mayim HaPanim L'Panim

"Just as water reflects a face similar to the face of the one who looks into it - if the face is happy, the reflection is happy, and if the face is sad, the reflection is sad - so does one man's heart to another.  If his heart is positively inclined towards his friend, his friend's heart will also be inclined positively, and if he feels negatively about his friend, his friend will feel similarly."

(Metzudat David Proverbs 27:19)