Why does Dr. Strauss Think Charlie would be a good subject for the experiment

Dr. Strauss thinks Charlie will make a good subject because he's motivated.

Dr Strauss said I had something that was very good. He said I had a good motor-vation. I never even knowed I had that. I felt good when he said not everbody with an eye-Q of 68 had that thing like I had it. I dont know what it is or where I got it but he said Algernon had it too. Algernons motor-vation is the chees they put in his box.