Why do people say you can be whatever you want to be?

Because they mean it in a realistic way. In different career options you can become who you want to be, with a LOT of work and dedication to something. However, you couldn't just wake up one morning and become a super model. It doesn't work like that. I couldn't just start acting from nowhere. You build yourself up. But for particular things such as modeling or becoming a super model, you have to have the right face, body and style. With other things such as PR's, doctors, or even nurses, you can become one of those with the right mental attitude and dedication. So that is what people mean by saying you can be whatever you want to be. You have to think logically.