I would be interested to know in what context a person might be saying this line. I think the quote suggests that person is shaped by the people around that person. As human beings we are profoundly affected by our experiences with our family members as we grow up. We are influenced by our friends as we go off to school and other activities. We are shaped by our choice of mate and the life created with that person. Human beings are in a constant state of adaptation to their situations, and those situations have an inevitable affect. That said, we also have some choice in creating the person we want to be. This quote puts the emphasis on the outside forces that shape a person.
You could analyze most characters in literature by evaluating how that quote is true for them. What other people/characters in a text influence and shape the nature of the main characters? To what extent? For what thematic purpose? It could become an interesting character study.
This quote reminds me of a short story I once read. An old man sat at the top of a mountain overlooking a town nestled in the valley below. As travelers would come by, they would look down at the village below and ask him what kind of town it was. He asked each traveler the same thing: "What kind of town do you expect to find?" If they said there were probably a bunch of thieves and pickpockets in the town, the old man told them that's what they would find. If they said it was probably not a friendly town, the old man told them they would probably find it to be unfriendly. If they said they expected to find a town of kind, friendly people, the old man told them they would undoubtedly find it to be so. The point, of course, is that we place our own expectations on others and treat them accordingly. "I am the person you make me" says essentially the same thing--if you expect me to be a bad person, you will see only the bad in me. Whatever you expect me to be, you will find evidence to support your opinion. It's a great reminder that we often have the power to bring out the best in people simply by expecting the best from them.
i think it means that if someone treats you bad all the time then thats what you will be (bad)