Positivity involves lying to yourself?

I've been reading about positive thinking and affirmations and I'm not quite sure I understand how it is alignment with reality. For example, from Susan Jeffers' book 'Feel the Fear and Do It Anyway', the phrase "i hope [this thing] will happen" is considered negative and has the standpoint of a victim, while "i know [this thing] will happen" is considered positive thinking. If don't really know that [this thing] -- getting a certain job, winning the lottery or meeting a certain person -- will happen then I'm not speaking in accord with reality and am being dishonest. I have trouble making myself believe things that I know are not true. Am I viewing this from the wrong context?