It can be difficult to recognize an agenda or bias when

There are many factors that can make recognizing a bias hard, but one of them is if we have the same bias. 

Say for example, that one person thinks that taller people are smarter and they listen to a speech that makes the same statement - they can then think that it's just confirming what they know, and can be a real fact instead of their bias. This will make it harder for them to recognize the bias.