@Soufiane Amanzoul what I say may not fit all use cases but the customer mindset from my perspective is all about having a service oriented mindset. Basically, every conversation you have a developer (customer) needs to start with acknowledgment of their problem, empathy, listening more/talking less and finally treating them as if you would treat a real customer who is paying you to use your product.
Again, may not be easy to apply across the board but anyone can work towards building that mindset. HTH!