Why do Graff and the unknown voice think it's important to keep Ender isolated in Chapter 5?

The men actually believe that the fight backfired, and that Ender might be too isolated. Regardless, they realize that they can do little for him, because if Ender comes to believe that anyone will ever help him out, he's "wrecked." Ender needs to know that there will never be an "easy way out," or else he will not become the commander they need for the upcoming war.