How Bad Company Corrupts Good Character

Bad company corrupts a person's good character. (1 Corinthians 15:33)

A person's character is composed of their:
1. Mental attributes (how they think) 
2. Moral attributes (the standards of their behavior)

Therefore bad company destroys a person's mental attributes by making them think in a manner that is not in alignment with God's Word.

Bad company also makes a person do things that are below the standards set by God's Word.  

A good example of this is seen in the Garden of Eden where Eve's bad company, in the form of the serpent, corrupted her character by:
1. Changing her mental attributes
Eve's thoughts about the Tree of the Knowledge of Good and Evil changed 
from "God has said that we should not eat or touch the fruit of the tree in the middle of the garden" (Genesis 3:3) 
to The tree is good for food, it is pleasant to the eyes and it is desirable to make a person wise (Genesis 3:6) 

2. Changing her moral attributes
Eve's standards of behavior towards the Tree of the Knowledge of Good and Evil changed
from Not eating or touching the fruit of the tree (Genesis 3:3) 
to Touching the fruit, eating it and giving it to her husband to eat. (Genesis 3:6) 

This Christian principle of Bad company corrupts a person's good character (1 Corinthians 15:33) contributes to numerous addictions since many of the addictive substances are not meant to be touched or consumed. 

In addition, this principle can be used to protect a person from destruction in many other areas of their life. For example, hanging out with the wrong crowd can make you start thinking about your spouse or your boss differently which can lead to you behaving differently towards them and thus destroying your marriage or career. 

Therefore, correct your crowd if you want to correct your character. 

Correct your offline crowd or company made up of the family and friends that you spend time with and your online crowd or company made up of the blogs and websites that you spend time reading so that you can influence your mind and morals positively.