Because most of us are basically good we don't expect others to be otherwise.
So when people lie to us and cheat us we are taken by surprise.
There are people out there who delight in malice and evil.
But because this is alien to us we are unaware of it.
This is especially the case if it is covered up with a veneer of acceptability.
Some people who embrace evil will delight in deceiving us.
And we swallow the deception whole.
Secretly they are laughing at us for being so naive.
So don't assume because you are good that others are good also.
This is plainly not the case.
Photo Credit: Dasha May Flickr via Compfight cc