Sustainability isn't an option; it's a necessity for survival.
The key is to set realistic customer expectations, and then not to just meet them, but to exceed them—preferably in unexpected and helpful ways.
I always tell people, if you want to be successful, find someone who has achieved the results you want and copy what they do and you'll achieve the same results.
Leadership is about making others better as a result of your presence and making sure that impact lasts in your absence.