"For they cannot sleep unless they make someone stumble"
This verse forms the first part of the warning Solomon has for those who come across the path of evil and those that take that path. He has said to avoid these shortcuts to the good life. They are destructive to your significance and meaning. He says that if you turn into their ways, then you will very likely be the person who they make stumble. These people see the world as a contest in which one person loses and one person wins. So, therefore, if they make you lose, they believe they have won. They do not believe in the everybody-wins philosophy. In fact, most of them would consider the win of an everybody-wins philosophy a loss.
This is the Hebrew word yashen which means to sleep. Their mental worldview is completely consumed with one person wins and another person loses. If they do not gain through making another person lose, then they believe that somehow, they have lost.
Solomon is saying to avoid these people because even if you are on their team, they will need to make you lose so they can win. They actually stay up at night thinking of ways to harm others so they can get ahead. This is the definition of unethical practices: harming others so that personal benefit can come to me.
Evil is not just that which is emotionally reprehensible; it is any action in which I must harm others for personal gain or benefit. We do not have to be shocked to see that something is wrong. In fact, when we see evil operate enough, we will no longer be shocked by it. But it is still wrong. This is why the Lord gave us the Ten Commandments – to declare clearly where the moral boundaries of harm begin.
This is the Hebrew word kashal which means to stumble, to stagger. Again, Solomon is pointing out the system that those who play on the evil side of the tracks have completely embraced: "I can only win if you lose. Therefore, I must make you stumble or fall or lose in order for me to be a winner.”
Solomon is trying to frighten you into avoiding this whole scene. You don't have to be connected to this group or this mentality. When evil presents itself as a viable alternative, don't go there. When the chance to steal from the company comes, don't. When the chance to commit adultery comes, don't. When the chance to get your way through violence or intimidation comes, walk away. When the opportunity to profit through lying comes, keep your mouth shut or tell the truth. When the chance to get ahead by forgetting or avoiding worshipping God comes, worship God and "lose" the time.