Know The purpose of some information. 

It is important to realize that everyone has an agenda, and everyone has a reason for wanting you to agree with him or her on whatever subject they are discussing or promoting.

If it is an advertiser, their agenda is pretty obvious. They want you to buy their product or use their service.

If it is a politician, they want you to support them and their political Party so they can win the majority of elections and determine the direction the country will take for the next few years. They may very well benefit in their personal finances and in other ways as well.

agenda (n) （潜在的或根本的）目的或动机  

politician (n) 政客   

finances(n) 财力