In the day when an ice cream sundae cost much less, a 10-year-old boy entered a coffee  shop and sat a table .

A waitress put a glass of water in front of  him.

"How much is an ice cream sundae?"

"50 cents," said the waitress.

The little boy pulled his hand out his pocket and studied  a number of coins in it. 

"How much is a dish of  plain ice cream ?" he asked.

Some people were now waiting for a table and the waitress was not patient .

"35 cents ," she  said angrily.

The little boy again counted the coins. 

I'll have the plain ice cream,"he said.

The waitress brought the ice cream, put the bill  on the table and walked away .

The boy  finished ,paid the money and left.

When the waitress came back ,she was surprised at what she saw.

There were 15 cents placed beside the empty dish . that wae her tip.

人的先入为主的想法会让我们失去很多东西。我们不要想当然的去决定事情。有些事情不要那么绝对。