Think before you speak!

“Think twice before you speak, because your words and influence will plant the seed of either success or failure in the mind of another.”
― Napoleon Hill 

NLP (neurolinguistic programming) suggests that our words are extremely powerful in influencing behavior, as well as feelings - not only of the people who hear our words, but ourselves as well.  If you say to Johnny, "You are lazy, you'll amount to no good," Johnny's attitude and feelings about himself will be influenced to match those words.  But worse, your own feelings will be negatively affected by that commentary.  This may seem curious, but in fact, observe your own emotions the next time you say something - positive or negative - to another person.