Assertiveness that works?

[Hatshepsut]

I feel that in the real world winning arguments is less about being "right" or "wrong" and more about a social dominance that I don't have and never have.

A statement which I believe is true and probably why assertiveness training doesn't work for everyone. The other side won't listen patiently while you "assert" your rights, but takes control immediately by using command tone of voice and "talking you down." You don't get a word in edgewise. Not everyone has command presence. And not having it is somewhat of a disadvantage, especially in societies like ours that emphasize the individual persona.

The only antidote I know of is making supportive friends and allies, and doing things to help other people. Helping other people isn't just "good," it makes it easier to get the needed friends. But I don't claim to offer advice; my life wasn't a paragon of success anyone would want to imitate.  

Stop telling yourself "I can't do this and I don't do that." Perception is reality.

The first statement may or may not be good advice, depending on its context. The second statement is definitely false. Perception is not external reality and we do not have the power to create our own reality. If that were true, then no one in the world would be in a bad situation because they would "create" a better one. Just because Stephen Hawking could be a physics professor despite quadriplegia doesn't mean everyone else can do it, and ditto for the many other Horatio Alger stories we love so much in the USA.

If the first statement simply advises against sitting on one's rumpus, then it might be OK. Undesirable situations and presence of limitations or frailties don't excuse laziness or defeatism. It's important to select realistic goals, though, and stick to them, and expect lots of pain along the way. You have to fight and win some battles if you want social standing; there really aren't any shortcuts.