Speaking and thinking positively :
The ability of thought and speech are their own respective worlds. When one thinks and speaks positively he causes goodness to be brought to the world. When one speaks negatively, then he causes evil to fall onto the world. Accoridngly, one must accustom his mouth and mind to think and speak only positive thoughts and words, and by doing so he will actually cause this to occure.
The lesson in service of Hashem: Some people tend to think the worst in any situation. Doing so can actually Heaven Forfend lead towards those outcomes. One must train his mind to banish thoughts of negativity and see the positive of every situation, and imagine the positive outcome. Likewise, even when it is appropriate to chastise another, one must beware not to use negative labels, name calling, and things of the like, which actually have the power to cause further damage.
 Or Torah [Maggid] 39