Accentuate the POSITIVE, eliminate the NEGATIVE

Since I was a child, my mother use to sing this song to her children.  We all recognized it, had it memorized, and understood exactly what she meant when she started to sing it.  I thought I would pass my mothers secret to stop murmuring and try to be happy.
 

Here are the lyrics:

 

"You've got to accentuate the positive,

Eliminate the negative,

Latch on to the affirmative,

And don't mess with Mr. in-between!"