However, sometimes the desired behavior is beneficial to the requestor but also detrimental to you. In order to get you to do it anyway, they attempt to use clever argumentation to persuade you that the desired behavior is actually beneficial to you (when it is not).
In other words, we are all bombarded, on a daily basis, by attempts to make us behave irrationally.
This is a risky situation, because our own irrational behavior could be harming us in ways we do not perceive. We must therefore defend ourselves against these attacks. In this case, the best defense we have is a working knowledge of formal logic. Logic is a martial art for the mind, or, as I like to call it, "Brain-Fu."
To quote Thomas Jefferson, "In a republican nation, whose citizens are to be led by reason and persuasion and not by force, the art of reasoning becomes of the first importance."
In my opinion, the best way to learn the art is in a formal class at a university. But if you are inclined to self education here are some resources:
A Wikipedia Overview
And some other books.
Knowledge is power. Be strong!