One outcome of that equation is disaster, possibly death. The statistics show that disabled children are much more likely to be abused by caretakers. It has been my observation in therapy with mood disordered children and their families that the abuse and neglect that occurs is more emotional than physical (but that is likely because these are people actually seeking help). The best outcome for a fragile person is to have an extremely loving and supportive parent/caregiver/partner. The perfect pairing would be with someone who is committed to and is actually walking with Christ each day, every hour. In those cases, the fragile person may bloom or at the least be able to function in a fairly normal appearing manner. Paired with a toxic person, symptoms worsen, meds increase, functioning decreases and the behavior associated with the disorder escalates to the point where there is danger to self and/or others. This is not to say that someone with a disorder that is not well-managed could not have this same outcome in a loving stable relationship with someone. It is more like having a low fire going, one that is managed but still glowing, and someone deliberately pours gasoline on it. In some cases, the toxic person may find themselves getting injured.
Have you noticed that toxic people often pick out a fragile person to attach themselves to? Sometimes this is subtle, such as a sexually abuse survivor who has someone in a position of authority over them who is just inappropriate enough to make them uncomfortable, e.g., mildly suggestive comments that no one else overhears. Sometimes it is much more tragic – such as in abusive marriages where a partner kills the other.
Do you make snide remarks, laugh at the foibles of others, take glee when someone you dislike gets their comeuppance, feel justified in ranting at people who don't do exactly what you want, and in general are a demanding intolerant person? Watch yourself – you are going down the slippery slope to the toxic pit. God can pull you out, but you will find a lot of company down there in that pit who will find you quite hilarious and justified. Please don't believe them. You cannot walk in peace and love and behave in that manner. But then, maybe you are a fragile person who has become toxic and need your own help (watch for a future posting).