Boundaries are such an important thing. There are so many things that they can protect from, including manipulation and co-dependence. Especially co-dependence. I've had alot of trouble creating my own, but I know from experience that going around without good boundaries can attract a certain type of person who will keep pushing to see how far they can transgress them. They will turn you into a doormat if you aren't careful
For me it was childhood bullies who first started that crap, but in hindsight I've come to see that it was certain people throughout my life who were doing that sort of thing. Almost all of them came in the guise of friendship. I'm kind of lucky in that the last decades' isolation eliminated almost all the controllers from my life, and distanced the ones left. So I get to pick and choose which relationships to continue with, and which ones to let drop off.
For me it was childhood bullies who first started that crap, but in hindsight I've come to see that it was certain people throughout my life who were doing that sort of thing. Almost all of them came in the guise of friendship. I'm kind of lucky in that the last decades' isolation eliminated almost all the controllers from my life, and distanced the ones left. So I get to pick and choose which relationships to continue with, and which ones to let drop off.