To understand the effect of negative words, think of yourself as a glass of water and a negative word as a drop of food coloring being dropped in. Only a little is needed to contaminate. Most esteem issues can be traced back to some negative statement. To dilute, there must be a constant stream positive words being poured in.
Proverbs 18:21 The tongue has the power of life and death, and those who love it will eat its fruit.