This question troubles many of us because it is very hard to answer. Some believe that you are born with it. Others think that your identity is shaped by culture , & then many believe its shaped by personal choices. I think they all contribute in their own way.
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My culture has a bigger impact on identity than my birth. You are around culture so much that you grow accostumed to it and make it a part of who you are. I was raised in a culture were a man must always show respect to women no matter what happens. This shaped me up to become a gentlemen and the man i am today.
For me, personal choices contribute the most to my identity. The reason being that I always CHOOSE to do something. I choose to follow my culture, I choose who I want to be around and I also choose what I pay attention to. Everything we do we chose to do it consequently adding to who you are as a person or who you become in the future.