Explain the following quote, "isolate him enough that he remains creative otherwise he'll adopt the system and we'll lose him".

I think Graff says this. Graff knows that Ender is different. Ender is creative and thinks outside of the box. Graff fears that Ender will become complacent and part of the system should he be integrated too much. He wanted Ender to stay on the "edge": to have the ability to improvise under pressure.