I Believe -

 Talking about core beliefs with friends and clients lately. Mine are, and have been since I was a teen (at least that's when I recognized them): 

Be fair

Be true

Do no harm

Three phrases that resonate with these are: 

That which we persist in doing becomes easier to do, not that the nature of the thing has changed, but our ability to do has increased. (Emerson)

If good is white and black is bad, then all my friends are grey or plaid. (Grandma Jensen)

Sometimes we're so busy existing that we forget to live. (13th Ward RS)

Yours?