Staying away for toxic people is a good idea and recommended for most people because knowing how to deal with them is not something the average person can handle.
Identifying a toxic person is not as easy as it seems. Jeri found herself in a toxic situation and had to extricate herself. If anyone has never been in that situation when they are the exception rather than the rule. Wake is correct that it can take years to rid oneself of the toxins from toxic people because they inject their poison deep inside you.
The worst about toxic people is that they drag you down with them and essentially trap you with their depression and negativity. Once you are depressed it is much harder to find the willpower to escape.
There are some good books that explain how interactions work and how to deal with toxic people. Most of them play mental games where their reward is to make you feel bad. These are usually done through guilt of some sort. Guilt because you as a good person are not there to help them out in their hour (make that lifetime) of need or because you have things better than they do and therefore you are the fortunate one and are obligated because of your fortune to assist them. There are variations but that is the primary game and motivation behind it.
Please note that toxic people might say that they care for/about you but that is a lie. They are utterly self centered and only care about themselves. They will tell you things to manipulate you into doing what they want. None of it is to your benefit and it always ends up costing you in emotional, time or fiscal terms.
Knowing how to break the cycle is crucial for you own well being and recognizing that it exists is the first step. Westwall intervened and broke the cycle for his friend. If you see someone in that situation speak up. If you are in that situation reach out to a genuine friend. Toxic people are never your friend in real terms no matter how long you have known them.
Good topic, Wake