Every aspect of our personality, our thoughts, our emotions, and our actions stem from our mind. The brain of a young child is to a large extent an open book waiting to be filled with impressions and narratives determining its future. This then happens throughout life in a constant interplay between external impulses and inner thoughts, shaping what kind of person we will eventually be.
You will become what you think
Modern neuroscience and Buddhist wisdom agree that our thoughts affect who we will become, and who we are today is to a large extent a result of our previous thoughts.