What Is Your Margherita Pizza?

So we can judge a pizzeria on how well they make a Margherita pizza, and a coffee shop on their espresso. What about your profession? I am wondering this myself. There are a lot of personal trainers out there, and a lot of gyms. Each has their own menu of offerings, and their own specialties. But what is that basic, simple, product or service or behaviour that we offer that really defines our performance?