Humans have an amazing ability to adapt to bad situations. Our minds can take terrible situations and slowly normalize them, leading us to cope and even find happiness when our circumstances change for the worse. This ability allows us to have contentment in times of plenty and times of little.
This same mental ability to reframe situations can take a darker turn, though. A person of good character can slowly morph into one who accepts evil as his new normal, simply by changing his social situation to one where he is constantly immersed in a culture of crud.
It’s always wise to remember that bad company can corrupt good morals.