They are real limited.

When someone has almost perfect control over what they let you see of who they are, then you do not really know them.

So . . . can you have a real relationship with someone whom you do not really know? Not in my book.

Actually, people on line do not have quite perfect control over what they reveal, and, eventually, who they are can start to leak out. If you know someone online who does not have any major faults, then you do not yet know them, and your relationship with them is not real.