I.E. Say your brother calls you and says that the Pentagon has been hit and fearing that it's true you believe his lie and spread it around spreading a lie without checking it out when you could have just found out the lie.
...or...
Your friend tells you that Osama bin Laden (or someone everyone hates) has been killed and tonight is going to be a party. Hoping its true you believe him without thought.
These reasons do not mean they are in anyway true yet since you so badly want or don't want to believe it you take it without thought. It is human nature...