When your kid achieves something, you expect him to do it either as well or better the next time.
Before you even notice, you will get used to him overachieving. And the more he will prove successful, the less you will pay attention, and sometimes even care less.
The same goes with customers.
And the similar the consequences.
As with your kid, your motivation to do good might fall down in proportion to the lack of interest / recognition of your client.
The problem in this case is not your client…but you.
Overdelivering is fine but you need to communicate. It does not stand out by itself.
If you want to keep him interested / impressed, you need to tell him what an achievement it was, why it was so exceptional and what enabled you do it, so that he keeps on valuing it.
This is all about communication.
If people were expecting a happy ending – « they got married and had plenty of kids » – from each movie, I bet no one would bother seeing movies anymore, don’t you?