Garth Callaghan has written thousands of napkin notes to his daughter. Now he's challenging us all to write 21 to show our love – one per day through Thanksgiving.

When it comes to relationships with loved ones, it's the little things that make them so rich and special. A "thank you" for a favor. A compliment on a job well done. A helping hand to make an unpleasant task go faster. Or, as one dad discovered, a daily note on a lunchbox napkin.

When Garth Callaghan's daughter was in kindergarten, he began writing a short note on a napkin every school day and including them with her lunch. For Garth, it became a habit, and for Emma, it became a fun daily surprise to see what wisdom or humor the napkin note might impart.

When Garth was diagnosed with metastatic kidney cancer, the notes took on new significance.

Garth has had four cancer diagnoses in the past three years. He's fighting, but he's also worried that he may not live to see Emma graduate. So he's doing all he can now to prepare her for a time when she may have to live without her dad. That includes writing napkin notes in advance – enough to get her through her high school graduation. In all, 826 napkin notes are stored in a special box, just in case.

Some of the napkin notes offer fatherly wisdom:

Dear Emma, Your best teachers are probably the ones that frustrate you the most. Love, Dad. PS – not all teachers are in front of a class.

We rise by lifting others.

Others provide words of encouragement:

If it were easy, everybody would do it.

No matter how you feel, get up, dress up, show up and never give up!

Sometimes Garth shares a favorite quote with Emma:

With the new day comes new strength and new thoughts. – Eleanor Roosevelt

Making mistakes is better than not doing anything. – Billie Joe Armstrong

And sometimes it's just a personal note about something happening in Emma's daily life:

Happy ½ birthday! I can't wait to teach you how to drive. Love, Dad.

Dear Emma, One of the most beautiful things in the world is watching you round the bases. I LOVE TO WATCH YOU PLAY! Love, Dad.

When Garth began sharing the napkin notes on his blog, the response from friends and strangers alike was huge. So popular were the daily notes that Garth released a book, Napkin Notes: Creating a Daily Connection With Those You Love, which has been picked up by New Line Cinema to be turned into a movie.

You can read more napkin notes, learn more about Garth and offer him your own words of encouragement for his cancer fight by visiting his blog at www.napkinnotesdad.com.

You can also join in by writing your own napkin notes during Garth's "21 Days of Thankfulness" challenge, which begins Nov. 4.

Garth has written thousands of napkin notes, but he knows not everyone can match that feat. So he's urging us all to write just 21 notes – one per day through Thanksgiving – telling a loved one why we're thankful for them.

Garth knows he may not be there for his daughter when she graduates from high school. He's taking that knowledge and using it as a catalyst to connect with her now and leave a legacy for her to continue discovering after his death.

As for the rest of us? It's pretty easy for feel sure that we'll be here tomorrow, but our futures are no more guaranteed than Garth's. If we take a cue from him and write notes to our loved ones during 21 Days of Thankfulness, we can we can leave a tangible legacy for them to remember us by.

And maybe we'll find the note-writing so easy and so satisfying, and enjoy the connection so much, that we'll keep doing it, just like Garth.

Learn more about 21 Days of Thankfulness

Originally published June 17, 2015