Has your firm ever missed the mark on a client matter -- and the client is still with the firm? In truth that question could be answered "yes" for many of your existing clients.
If clients valued excellence in legal services over the relationship they would jump ship every time an attorney did not perform in absolute excellence. Granted, the quality of legal services has to be in the realm of good to best, but I hope you see my point.
Do well at your work and do better at your relationships. Loyalty only knows two extremes; We are loyal to our friends and we are loyal about our enemies. Everyone else does not matter.