There are people that routinely cause damage to others without deriving any benefit to themselves.  They do not even consciously think they are causing harm. They are much worse than thieves or similar criminal types. 

You might be vaguely aware of these types but you forget about it. 

And you might even pride yourself that you do not mind hanging out with lowliness. But you forget this very important principle. For these people consistently cause damage to others without gaining any benefit to themselves. It is not an accident, but a pattern.

Slowly imperceptibly you lose what ever good traits you have by hanging out with these types.

There is a sort of "evil inclination" that says to you you do not want to be a "baal gaava" [person with pride] so you hang out with low lives thinking you will bring them up or at least not lose. But that is exactly the trick. --To get you to hang out with people whose ultimate effect is to cause you to lower your standards of decency .