According to Fitzpatrick, thank-you notes should be sent in a variety of scenarios. A thank you note is showing appreciation and acknowledgement of either something done for you or given to you.

The thank you note you write (or don't write) after a job interview can mean the difference between landing a job or not.

Handwritten Notes Are Still the Best Way to Reaffirm Your Customer Relationships. Here’s How to Write a Good One There’s nothing like a personal note written with real ink on paper.