While explaining the difference between flattery and appreciation, Dale Carnegie references this quote. He mentions the importance of appreciating people and how much of a positive impact a genuine appreciation can make on people, by giving some good examples.

The difference between appreciation and flaterry? That is simple. One is sincere and the other insincere. One comes from heart out; the other from the teeth out. One is unselfish; the other selfish. One is universally admired; the other universally condemned.

As you can see flattery is highly negative, whereas appreciation is highly positive. That is summed up nicely in this quote to warn us against potentially negative friends. What we should be afraid of is not the enemies but the friends who are deceiving us by flattery.

We should understand this difference and always give honest and sincere appreciation. 

Amazon link to the book below.