“I’d like you to do chlorine too.”
“But I shouldn’t have to do chlorine. Chlorine was extra homework last time. I got Argon. I’ll do Argon. I don’t have to do extra homework today, so I shouldn’t have to do chlorine too.”
“It’s true, you didn’t earn extra work today.”
“So I don’t have to do chlorine.”
“If you do chlorine we’ll have the full set of elements.”
“But do I have to do it?”
“I’d like you to do it.”
“But do I have to?”
“No.”
“OK I’ll do it.”