Being is an ever unfolding process of becoming.
It is what it is and you are what you are, but "it" or "you" is more of a fluid process than a static thing.
I've encountered a few people over the years on various philosophical themed blogs, who are opposed to such things as "self-improvement" and "inner cultivation" or basically any attempt to change yourself in some way. Those who espouse such views are usually Westerners under the influence of Eastern philosophy.
Their reasoning is that you are what you are, and it is not possible to be anything but what you already are, therefore any attempt to do so is unhealthy and inauthentic. That trying to improve yourself, is an attempt to change yourself into something that you are not; effectively resisting your true nature, akin to going against the genuine current of who you are; and that you do not need to improve or change because your inner nature is already perfect in and of itself, if you would only realize this.
It always angered me to hear this, because not only did I think they were dead wrong, and that their reasoning was based on a flawed understanding of personal nature, and the true nature of being and becoming, but that such advice was actually detrimental to anyone who listened to it and tried to apply it to their own lives.
Why? Because self-improvement and personal cultivation is less about changing who you are, and more about discovering who you are and increasing your overall awareness and understanding of the world. It's like the tuning of an instrument, adjusting your awareness so that it achieves harmonic resonance with your true nature, and then learning to play the instrument well.
So it's less about changing who you are, and more about centering and refocusing your awareness, similar to a camera, on what is true. A camera is much like your nature, it is what it is, but the quality of pictures taken, whether they are blurry or clear, depends on the quality of your awareness, and the ability to bring the image into focus.
I exercise not only to become stronger, but because it clears my thinking and makes me feel better. It's very much like eating or sleeping, a necessary function. I feel the same way about reading. So perhaps you could say that the pursuit of knowledge and fitness, self-improvement and personal cultivation, for some, is an expression of their true nature.
What is your true nature?
It is your essential being, or personal essence actualizing itself through the process of becoming. Your true nature, or essential being, is an energy overlapping your entire body and consciousness, moving in a specific direction or pattern unique to yourself, much like a magnetic bearing on a compass, a point of reference out of which all else proceeds. It is your particular direction, or unique pattern of movement, current of energy, or personal flow of being, influencing thinking, feeling, doing, and the processing experiences.
Your inward nature, is not a fixed entity or solid structure, but is more of a moving energy, like a current of wind, water, or the energy of fire, which interacts with its environment in which both are modified by the process; being both influenced and influential, affected and affecting, attracting and repelling, being and becoming, self-actualizing itself through the experience of living, learning, and interacting.
For instance, the nature of sand is sand, the nature of water is water, but when water interacts with sand, each is modified by the interaction. True?
The same could be said about one's genuine nature, it is what it is, but when it interacts with different things, and is exposed to different environmental and cultural influences, just like the water and sand, it too is modified ever so slightly, even if it is only a subtle shift of awareness. And a modification, or adaptation, is not always a bad thing, sometimes it just is what it is, a necessary change, an unavoidable reality.
Therefore, self-improvement and personal cultivation, rather than taking one further away from oneself, could actually bring one closer to oneself; self-actualizing your genuine nature through an adjustment of awareness.