It's hurtful to trick people.
Bob sees that his classmate Tim has delicious looking brownies packed in his school lunch.
Bob wants to eat a brownie.
Bob asks Tim if he would be willing to share one of the brownies with him.
Bob tricks Tim into giving him the brownies, then he eats them all.
Tim agrees to give Bob a brownie and both boys enjoy eating them.
Tim feels sad and Bob later gets in trouble for taking the brownies.