Cameron Newton is very excited about the within-subjects approach. He says, "I'll never need to run large numbers of subjects, or opposing defenses...

Cameron Newton is very excited about the within-subjects approach. He says, "I'll never need to run large numbers of subjects, or opposing defenses again". However, Cameron has forgotten that within-subjects designs inside the game may consist of four objections. What are those Objections? Give an example of each of these four objections?