This is a curious rule and it took me a long time to learn because in fact at the beginning of my practice I felt the opposite.Professionalism required that you didn’t particularly like the people that you worked for or at least maintained an arms length relationship to them, which meant that I never had lunch with a client or saw them socially. Then some years ago I realized that the opposite was true.
I am talking about a client and you sharing some common ground. That in fact your view of life is someway congruent with the client, otherwise it is a bitter and hopeless struggle.