“Each day, we wake slightly altered, and the person we were yesterday is dead,” said John Updike. It's similar to how scientists explain teleportation in Start Trek: each time Captain Kirk teleported himself, he was literally split into molecules and re-assembled from different molecules somewhere else. So technically he was killed and cloned each time.
While sleeping is of course not that extreme as we still wake up in the same body, I definitely agree that we are a different person every day, possibly every moment.
Oftentimes, we limit ourselves by those past experiences, not being able to step outside of the comfort zone or the image of ourselves that our brains create.
Let me explain this with one of the most loved/hated Game of Thrones characters, Jaime Lannister. In the beginning of the series, he does terrible things, driven by his self-perception of "King Slayer," "the most dishonorable man." He has nothing to lose. But throughout the series Jaime realizes he can start over and be the man he aspires to be.
Another example is what one friend of mine who has weight issues once told me. She said, "I'm already overweight, it doesn't not really matter if I eat this cake or not." Maybe she is somewhat right, and in a larger scheme of things this cake doesn't change anything. Nonetheless, we should not swap the reasons with the consequences. Jaime was called "the King Slayer" because of his past choices, it doesn't mean he had to continue to act dishonorably; my friend didn't have to eat that cake because she was already overweight.
The self is constantly evolving. Our molecules get replaces by a set of new ones. Our emotions fade, and the new emotions rise. Past choices should not affect your choices of the present moment. You are who you are right now, in this very moment. The rest is just a memory of who you once were.