What is it that makes up you? Take a moment to really let this question sink in.
Is it your personality traits, your outward appearance, your job, your university, your bank account?
What are you? Who are you?
If you answered with personality traits, let me ask you this. Are you the same as you were 5 years ago?
If you answered with your outward appearance, do you look the same as you did when you were 10?
If you answered with your job, how long have you had that position?
None of these things are concrete or unchanging enough to base who you are off of them. They are all circumstantial. Just as your height and personality traits and interests have changed over the years, so has your conception of yourself. We often say that we are "not the same person" as we used to be, and we are absolutely correct. If you think about it, you're not the same person you were yesterday, or an hour ago, or even one minute ago. Each new thought or piece of information you absorb changes you. We, as the saying goes, "learn something new every day". In learning new things or hearing new things we adopt new beliefs and shed old ones, thus consistently existing in a state of change.
Considering all of this information makes the question of what makes you up even more complex.
I asked myself these questions and realized that walking around each day and thinking led me to a conclusion that a "me" existed in objective reality. I never stopped to question it, I just knew it. If someone would have asked me this question I would have said something like, "I can see myself in a mirror and move things around me so of COURSE I exist." But when you stop to ask this question a little more specifically, things start to get foggier. Circumstances change all the time and people change all the time, so is a consistent self ever really existing? If you still answer yes to this question, can you answer the question of where this "self" exists? You might think your "self" is your body, but if that's the case, how can people experience head trauma only to become completely different people? Is your self your brain? If so, would your personality still exist if your brain was floating in a vat of fluid? All of these questions simply proved to me that the more I pursued or pondered them, the less I realized I knew. Therefore, I concluded that I cannot reasonably assume that a "me" even exists at all.
I came to this realization and my reality was shattered. It was terrifying and liberating at the same time. Once I glimpsed this startling truth I knew I'd never be able to think or live the same way again. It's a little scary to have nothing to identify with, but also freeing to know that you never have to hold yourself to ANY standard again. For example, I've been a smoker for quite some time. Always trying to quit and always failing. Therefore, whenever I'd start another one of my righteous quitting stints, I'd have in the back of my mind that I've done this so many times and failed each time, I just have such limited self control, etc, etc... and in "knowing" these things about myself, I was helpless because of them. I failed every time before that so it was only a matter of time before I failed again.
Another example would be the social anxiety I tend to have. "Knowing" that I am a shy person only causes me to act like one. What if I instead decide to experiment and tell myself I'm not shy? I have tried this and it works. With no conception of a set personality that I subconsciously honor and live up to, I am free to be absolutely anything.
It never crossed my mind to wonder if I was causing these attributes by "knowing" they exist, until very recently. If you really take a second to think of the hugeness of the universe and the pathetically tiny portion of it we understand, and how much of what we understand could be hugely mistaken due to literally everything being perception, it really is absurd to assume we "know" much of anything. Could we then reasonably assume that all this time, we have been wrong about ourselves? Holding ourselves back by holding ourselves to standards of what we did or didn't do in the past? We've all heard the quote that "the best indicator of the future is the past" and you know what? I say fuck that quote. I say that quote is the denier of change, which is inevitable. The only thing permanent is impermanence and the sooner we all realize that, the better off we will be. Try to think of just one example that proves that statement wrong.
The best way to be happy and live to your fullest potential is to approach each day with a blank slate. No day is ever the same so no day deserves to be categorized the same as any other day. Likewise, you are not the same today as you were yesterday, so why hold yourself to the standard of how you were yesterday?
"To affect the quality of the day, that is the highest of arts." -Henry David Thoreau