When you begin the Customer Development process, you chart how you are performing.
The key to Customer Development is to have unique tactics for unique audiences. If every customer gets 40% off, you aren't Developing Customers, you are managing campaigns.
If you offer some customers a discount and not other customers, you are implementing a Customer Development tactic. We can debate whether this is right/wrong. But you are Developing Customers.
In the image above, I color cells blue if there isn't a personalized Customer Development strategy for the intersection between a customer audience and a marketing tactic. If the brand executes specific email campaigns as part of a Welcome Program, the intersection of Welcome (row) and email (column) are yellow.
There are five rows above, and six columns, yielding thirty (30) cells. In the image above, three cells are colored yellow. The Customer Development Index (CDI) is therefore 3/30 = 0.100.
In other words, you aren't doing much to foster Customer Development.