This is one thing that many people forget about sin. Many souls, who do not commit grave sins, might be content with a spiritual life in which they are committing minor sins. Actually, content might not be the perfect word however it does not bother them too much.
However, a soul that does not see minor sins with a great deal of repugnance, will in only a matter of time start to engage in sins that are much greater in evil and which will be darker in nature. Also, when it comes to sinning, a soul can fall into a abyss which has no floor.
Sin can take you to a very dark place. However, God always always has a Plan B. He always gives us a chance to turn it all around.