Things I've learned about Boundaries:
They are for me, to protect me. Not to control someone else. I can't make someone else do something. I can make a request of them. They always have the right to agree, disagree or talk about making a compromise. This has been the hardest for me to accept.
In setting a "consequence", it's not a punishment, it's still about protecting myself and has to be something I can do. Again I can't make anyone else do something.
I absolutely have to follow through with what I say I'll do. It's for me and it helps me build trust in myself. If I'm not ready to follow through with say- leaving the relationship, I do not threaten. I whittle it down until I find something I know I'm willing to follow through on. It's a place to start. And the more I practice, the more I build up my boundary muscle.
Boundaries were not so helpful to me until I really got into working on myself. Mostly because I could set them but I had trouble holding them. And in hindsight, it was still about trying to control. When I started really working on me, everything changed.