Do you know what will happen if you put a frog into a pot of cold water and slowly raise the temperature? The frog readily adapts to the warming of water without ever sensing the increasing heat until death results. In the same way, as you ignore the small sins and put them into practice, your conscience will become increasingly numbed. As time passes the degree of sin committed increases until the unpardonable sins are committed. That's why it is very important for you to guard your conscience in even the smallest things.
"In view of this, I also do my best to maintain always a blameless conscience both before God and before men." (Acts 24:16)