If I have a dollar and you have a dollar; and we exchange our dollars,we only have a dollar each. If I have an idea and you have an idea; if we exchange our ideas, we have two ideas each
 
  假如你和我都有一美元钱，我们彼此互相交换这一美元钱，那么你我还是只有一美元钱。
   假如你有一个好主意，我也有一个好主意，我们彼此互相交换主意。那么我们就有两个好意思了。