@parados,
Is a boundary a container?
If a boundary is a container, and a boundary is not a difference, what is implied?
Is the cup that holds the coffee the coffee that holds itself?
Starting to get annoyed at how you are used to thinking?
Don't feel bad. Plato's Parmenides is meant as a mental exercise to learn the principles of predication. As far as I know, no one has figured out the dialog yet.
When you cannot distinguish in your mind, the three categories of names, you have no choice but to think nonsense.