After reading the comments some elaboration may be in order.
The more comprehensive answer is that you have to use grammar deftly. That means when you get it "wrong" you know it's wrong.
And let's also remember that how people actually talk is almost never in complete, correct sentences.
One of my favorite scenes from The Wire opens with Cedric Daniels speaking what we would call "proper" English, then when he's engaged in conversation by Damian Price, he slips into Baltimore street English so as to establish rapport.
It's brilliant writing, and if you handed it in for a grammar class assignment, it would come back with a lot of red marks.
Here's another example:
Stringer: Nigga, is you taking notes on a criminal fucking conspiracy?
"Correct": Shamrock, are you taking notes on our criminal conspiracy?
Freamon: I don't wanna go to no dance unless I can rub some tit.
"Correct": I don't want to go to a dance unless I'm actually going to dance.
Egad! Talk about stripping the lines of energy and vitality!
Bottom line here: I'm not going to reject your work for an errant whom, or a mistaken lie/lay/lay. But not knowing that affect and effect mean different things? That's a problem. Not knowing that reign in Spain doesn't involve water, that's a problem. There's absolutely no stylistic reason to get it's and its wrong. Or hair and heir. Let alone there and they're. When I see those, I know
You get those right so I know that "Nigga, is you taking notes on a criminal fucking conspiracy?" is exactly what you meant to say.