Do not “be” yourself.
When we learn to know someone we start to build an abstract picture of the person via observations of interior or exterior characteristics . These characteristics are properties we invent as abstract constructions checked against the ongoing observation of the person. Properties are indeed abstract notions but they may either reflect some reality or else be completely invented using fantasy. Fantasy being the ability to construct perceptions similar to observed structures in reality but then freed of the restrictive condition which existing in reality puts on the observations of the structure. Hence an observed elephant can become a fantasy object :a flying pink elephant that plays harmonica.For example “weight” is a property reflecting a reality but goodness is a personal evaluation on the basis of a personal moral it is not reflecting a reality .Obviously,the picture we construct of a person is not a faithful representation of it ,it is based on partial information ,using non-real properties, and it does not change with the person in time,except for some discrete set of adjustments one can make from time to time ,so it is a frozen fuzzy picture based on past thinking.Now the observed person is free,it has free will on the abstract level (“Die Gedanke Sind Frei!”) but the image we construct in our mind is not free it is manipulated by us and fixed . Therefore we will be often surprised by the unpredictability of “people” but that is in fact an observation of the difference between our image and the real person . The linguistic statement “getting to know someone” is really quite accurate ,it is a never ending process and in fact it is not necessarily based on correct observations ,hence not necessarily converging to a “good” approximation.
Now we also construct the image of ourselves ,this is the third part of the Self . First part being the living real being ,second part being the observer constructing the picture in the mind. Again we as a biological living entity have abstract free will (you can base this on the ability of random drawing information from the memory and constructing arbitrary new concepts with that information ,so in a sense free will results from us not being able to think reality and having to think via abstractions resulting in the creation of fantasy and then free will). Free will does not exist in reality as an object ,it is indeed abstract but it allows and directs actions on reality. Anyway the picture constructed of people and us does not have free will and that can never be pictured well because it is unpredictable,exactly because it is free ( see random thinking) .So we often surprise ourselves and our reactions in new situations will never be exactly predictable !
Thus,we never know even ourselves on the deepest level . In fact the more self-analysis the heavier the picture but also the stiffer the rigidity built in ,even with the above ideas explicitly known the picture of us is always a prisoner of our own mind .
So when someone tells you to be yourself he may mean you have to act as the image he has of you ,in the best case he means you should act as the image you have of you. Note that is different from saying “act as you please” because that is not according to the image you have ,so that would accord too much freedom to a person ,in fact then it would be useless to give this advice to someone and moreover it may create a feeling of disinterest from the advisor .
In conclusion ,to avoid the rigidity of your past self-analysis one should not be oneself …but be free from the cage of your own image.