Is it possible to change a persons personality through sheer willpower? If so, how?

Often I thought about whether or not a person can change their personality or not, more so due to the fact that I believe in the idea that we are born without any inherent personality and that personality is just a series of learned behaviors that help us navigate and interact with the world. But if that is the case, is it possible to just flat out change your personality whenever you want? Because if that is the case, I would love to be able to do so, since I believe my personality is pretty lackluster and I think it hinders my interactions with people.<br><br><br><br>Edit: I was talking about fundamental personality and not surface level behaviors, like a pessimist changing their mindset into being more optimistic because I know you can change behaviors like that.