Why is the child different from the Parent?

I can't count many times I've heard from either of my parents or actors that play parents on movies that their doing the best they can. So if us as the child has to accept that they are, why can't we (the child) tell them the same thing? What makes them think that we aren't also trying the best we can, that maybe we're just as stressed or whatever as them.

Mom's been yelling at me again. I know things are tight but she doesn't need to take it out on me. It's not like I'm not busting my ass trying to find a job. I can't just make one up, because if I could, I totally would.