Our expectation of results of what others do and even what we ourselves accomplish determines what it means to be successful. If what happens falls short of what we expect, we are disappointed. If, on the other hand, what happens meets our expectations, or even better, exceeds them, we define the outcome as successful.
So now if we assume everybody else thinks like we do, the success formula for performance is to always make sure to deliver more than we promise.
If you are able to deliver more than is promised or expected, then you will be successful. If, unhappily, you fall into the trap of over- promising and under-delivering, then no matter how well you actually do, it will never be enough. What you have accomplished will have limited value because the recipient of the service was expecting more.
Delivering more than you promise is easier to say than to do, but if you can manage it, you will have more success and you will have earned it.