Why Write Thank You Notes
Why is it now up to you to write this little note?
One reason is: To return the favor. One act of kindness deserves another.
Sure they probably already know you're thankful, but by stating it outright, you are giving another gift.
If that's not a good enough reason for you, how about this:
Recently gratitude has been the focus of scientific research and is actually proven to have an impact on your well-being. From the Wall Street Journal:
"...adults who feel grateful have 'more energy, more optimism, more social connections and more happiness than those who do not', according to studies conducted over the past decade. They're also less likely to be depressed, envious, greedy or alcoholics."
And it's not just adults who can use thank you notes as tickets to happiness. In a study of over 1000 teenagers, Dr. Jeffrey J. Froh, assistant professor of psychology and lead researcher of the new study, found that
"grateful students reported higher grades, more life satisfaction, better social integration and less envy and depression
...than their peers who were less thankful and more materialistic. 
Additionally, feelings of gratitude had a more powerful impact on the students' lives overall than materialism."
But just like exercise and diet, you need to do it a lot to reap rewards. According to the study,
"...one simple way to cultivate gratitude is to literally count your blessings. Keep a journal and regularly record whatever you are grateful for that day.Be specific. Listing "my friends, my school, my dog" day after day means that "gratitude fatigue" has set in, Dr. Froh says. Writing "my dog licked my face when I was sad" keeps it fresher. The real benefit comes in changing how you experience the world. Look for things to be grateful for, and you'll start seeing them."
So if you're reading this, you're off to a good start! Get started on those thank you notes and keep them coming. It's good for you and good for them.