A favourite of mine is a pseudo 'inspirational poster' quote:
Eagles may soar but weasels don't get sucked into jet engines
:lol:.
But a core tenet that I always try to remember and sometimes forget is one I posted very recently here at MT with regard to the brevity of life and the importance of retaining a sense of perspective:
"Out, out, brief candle! Life's but a walking shadow, a poor player that struts and frets his hour upon the stage and then is heard no more: it is a tale told by an idiot, full of sound and fury, signifying nothing.".
I have to say that if you ever need to delve into either inspiration, wisdom or plain truth about the human condition, you wont go far wrong with Shakespeare.