You will delight your customers by underpromising and overdelivering, i.e. going above and beyond what the customers expect.
Test: underdeliver, deliver to the letter, overdeliver on promises.
Overdelivering produces little meaningful increase in gratitude or appreciation.
A promise is a contract; you expect what was promised to you and nothing more (otherwise you would’ve asked for more).
Delivering to the letter is essential for maintaining reputation [MK: which is more important for the word of mouth than delight].
Generosity is not as important as fairness.
[MK: generosity advertised via the word of mouth leads to unrealistic expectations by new and existing customers.]