
Rule #1: When you can't decide what to believe, make the most useful assumption, and take the actions you would take if it was true. (For example: Is it more useful for you to assume that you are irredeemable and nothing can be improved at all and you should hate and act out against everyone all day? Or is it more useful to assume that you have some wiggle room, that symptoms can be strategically managed if you do your research, that small positive gestures toward your friends and family might make incremental improvements in your relationships, or even create new ones?)

Rule #2: Sometimes the best answer is to throw the question in the trash. Sometimes the best solution is to realize the problem doesn't matter. (Honestly I apply this to all the philosophical/existential concerns that used to bother me. The BPD mind generates WAY too many questions and problems, but you are NOT required to take action on them, nor are you required to assign significance to all of them.)

Rule #3: When you're splitting really bad (whether it's one person or the whole world), use The Scope of Lovable Things exercise (yes it's a thing I made up, but give it a chance). It's a simple conversation with your Inner Child. BE GENTLE. Here is a real sample from my own life (I always write it down like a dialogue)..... 

"I hate everything and everyone." 

--What about your friend's dog? She's very sweet and always gets excited when you visit.-- 

"Okay but that's literally one dog on a whole horrible planet." 

--Have you met other nice dogs? Is it okay to say when dogs are nice to you that you like them?-- 

"(Nods, still very angry and hurt)" 

--Okay, we like nice dogs. What about the vets that help the nice dogs? Remember when we saw that report where an old man was very sad because his dog was sick and the vets made it better?--

"(Nods, wants to cry)"

--Okay sweetheart, so we like nice dogs and nice vets who take care of them. Later we can look for more things we like if you want to. Is that okay?--

"(Nods, crying, but feeling much better)".....

^^All you're trying to do is widen the Scope enough that the vice-grip of the splitting mindset lets go. Crying is a good indicator that you can stop.