Is telling your young child (s)he can be anything she or he would like to without context, responsible parenting?

Yes. You shouldn’t close doors too early. They need to dream. Let their imagination grow. Learn the sensation of having faith in themselves. The joy of possibility. Young ones don’t do gray area well, so you either let them fly or chain them down. They’ll figure out soon enough that they can’t be a unicorn, but they’ll smile when they remember that they wanted to.