When I was six, I spent a summer with my grandma. One day, she asked me to go shopping with a list. A lady was there in the store. 

"Excuse me, I need to buy these, "I said, showing my list. She looked up and said, "Little girl, I'm Miss Change. There's no one here but you and me. I think you need to get them by yourself."

I went to the store every Tuesday and Thursday that summer. Sometimes she shortchanged (少找零钱) me. Other times she overcharged (多收钱) me. Going to the store was like going into battle (战斗). All summer long she found ways to trick me. But by the end of the summer, the shopping trip that had once taken me an hour was done in 15 minutes. 

The morning I was ready to run home. 

"All right, little girl," she said. "What did you learn this summer?"

"That you're bad!" I replied.

She just laughed and said, "I know what you think of me. Well, I don't care! My job is to teach every child I meet life lessons. When you get older, you'll be glad!"

Glad I met her? Ha! 

Until one day, my daughter came to me with homework problems. "It's too hard," she said. "Could you finish my math problems for me?"

"If I do it for you, how will you ever learn to do it yourself?" I said. Suddenly, I was back at that store where I had learned the hard way to add up my money by myself.