With whom?
Most of us, probably everyone reading this, has had a person or two in life you've forgotten to thank.
To check, ask this question: "What have I received from__________?
A teacher who made a big difference in my life
A parent who forgave me when I did something dumb
A relative who believed in me
A coach who guided me to be my best
A boss who gave me a chance with a job
A clergy person who helped me find my way
A friend who lifted me up when I was down
A room-mate who showed me how to dress
If in the same area, take that person to lunch and share your gratitude.
If miles away, phone that person to say "thank you." And thank that person from the heart.
Both of you will benefit.
P.S. Don't thank them via email.
If you need evidence for why expressing gratitude is important, see "Thanks! How the New Science of Gratitude Can Make You Happier," by Robert Emmons, Ph.D. (2007)