Can People Change?

I read somewhere that every cells are replaced in our body every 7 years, so in a way, every 7 years we’re a new person. But are we really? We grow and we change, but how much of that is real change and how much of who we are is the same? Every time I’ve moved, or started a new job, or met a new person, is a new opportunity to redefine myself, to make that first impression. And while we do change, to an extent, through growth and experience, how much do we really change?