Hi SD,
This is actually a complicated question and the answer somewhat depends on what the asker really wants to know.
No one is the exact same person in all circumstances with all people, it actually wouldn't be appropriate. Of course, we're going to be behave differently at our job than we would at a family party, or behave differently with our kids than we would with our friends. In our relationship with our kids, we need to keep it about their needs and not place the burden of our needs on our kids so we don't go there. But when we are interacting with our friends, that is the place where we will get some of our needs met, so that side of us can be expressed. So I think it can be a mistake to equate always being yourself with feeling like you will behave exactly the same way in all situations.
But I think the other way the question can be posed, and often is in therapy, is more of a when is it ok for you to allow your desires, needs and values to drive your behaviors? For you to behave authentically, driven by what you know to be true with your boundaries? You can behave differently in different situations but have it still be authentic.
One of the things I discovered about myself during my therapy work was just how driven I was by other people's needs. When I am with another person, then my focus would often be on what they wanted and what they needed. I was close to incapable of even realizing what it was I wanted or needed, let alone being able to express it or allow it to guide my behavior. And that's where the damage comes in. That I could be feeling one thing inside but behaving so differently on the outside.
My T created a safe place in which he didn't tell me who I needed to be, but made it safe to be whoever I was. I discovered myself within that freedom. So as I have grown in understanding of myself, I have also grown in my ability to be myself. I don't behave the same in every situation, but my decisions about how to behave are based on my feelings, my values, and my needs. So sometimes I'm not doing what I want to do, but I am doing what I choose to do.
As an extreme example, when my husband is in the hospital with heart problems, it can become quite scary for him. I am sometimes really scared also, but he doesn't need the burden of my fear right then, so based on my values of loving my husband, wanting to support him and my assessment that his need is greater in that moment, I conceal my own feelings (not suppress or deny them, just don't choose to show them) in order to be there for him.
But in another situation where its appropriate for my needs to come first, I am able to express my fears and needs.
But it wasn't until I got a LOT clearer about boundaries, so that I could know what was mine and what was another person's and learned to accept that I was human and had limitations that it began to be ok to let my outsides match my insides.
I still don't do it all the time, but I do it most of the time now and it works a lot better. When you learn to love and accept yourself for who you are (and yes, I understand the irony of my saying this considering what I just went to see my T about, what can I say, I'm a work in progress, always will be
) it becomes a lot easier to just be that person.
AG
I think if you put all those sides together you would get the real me but that was never the case. I think everyone gets to see a real part of me but not the full picture of me if that makes any sense. 
