There are many great lessons in this book; this is a favourite.
“Understanding the distinction between service and hospitality has been at the foundation of our success. Service is the technical delivery of a product. Hospitality is how the delivery of that product makes its recipient feel. Service is a monologue—we decide how we want to do things and set our own standards for service. Hospitality, on the other hand, is a dialogue. To be on a guest’s side requires listening to that person with every sense, and following up with a thoughtful, gracious, appropriate response. It takes both great service and great hospitality to rise to the top.”
Before you spend any time or money on your marketing, ensure that you provide hospitality within your restaurant, not just service.
But don't take our word for it; read the book.