Praising and slandering are opposites. It's hard to stay in the middle. Praising someone to a limit may not give them the ego boost, however trying to manipulate someone into praising themselves would be like hitting the ego nail right on the head. A pat on the back simply helps with the confidence, like a job well done.
Remember a smile in some places may not mean what you think. In the same way we must not get into the ideas of thinking praise is good.