Imagine your favorite toy. It gets old and broken. You fix it with new parts. Then you fix it again until every single piece is different from the original. Is it still the same toy? This question is called the Ship of Theseus.
The Puzzle
Our bodies are like that toy. Every few years, almost all our cells die and get replaced by new ones. Your skin, blood, and bones are constantly being rebuilt. If every part of you changes, why do you feel like the same person?
Two Answers
Some people say identity means physical stuff. If your body was completely swapped for an alien copy made of identical atoms, it would be a new you. Others say identity is about memory and story. As long as your memories connect smoothly to each other, no matter how many parts change, you remain the same person. It is like a dance; the dancers change, but the dance stays the same.