DarkMatter2525 is one of my favourite online satirists. This is an interesting metaphor (you can guess for what.)
When trying to make decisions in life, you want to make them on the basis of as much information as possible. For almost every decision you could make, there are different ways of framing things and items you could rack up on a pro/con list.
There are two dangerous tendencies which can get in the way. The first is our tendency to confirmation bias. So once we see something as a good idea, we tend to only see the good things in it (the same thing is true for things which are "obviously" bad ideas). Gathering all of the information from both sides usually takes work.
The second tendency is to take the mental shortcut WYSIATI (dubbed by Daniel Kahneman; What You See Is All There Is) where we take the information presented as the full story and never feel compelled to go searching for more information.
So when you're presented with someone offering you only one side of the story, focusing on the good and saying nothing of the bad, that's your cue to do some more homework.