From Wikipedia:
A mantra is a sound, syllable, word, or group of words that is considered capable of "creating transformation" (cf. spiritual transformation). Its use and type varies according to the school and philosophy associated with the mantra.
However, for anyone who lives in the REAL world: A mantra is simply something you say to yourself over and over again--like "Murder is illegal, murder is illegal, murder is illegal."
"Murder is illegal" is my favorite mantra. It's humorous and it also helps me keep my (thoroughly non-violent) temper from time to time.
I also have a few 'situational' ones.
So do you have a 'mantra' of your own?
If not then come up with some and share them.