We have two kinds of grammar: prescriptive and descriptive.
Prescriptive grammar tells us what English is supposed to do.
Descriptive tells us what people really do.

I went to a Vietnamese restaurant with some of my old Vietnamese students. It is called Pho Tan Vinh. They serve the soup, pho, because that is what Vietnamese food is supposed to be.
But when I am in Vietnam nobody ever says, “Hey, let’s go eat pho.”
We do eat a lot of beef and fried eggs in little cow plates. That’s what people really do.
(We had some Thai friends coming along too, so I ordered pho to kind of show them what “Vietnamese food” is.  The Vietnamese got the steak and eggs on the cow plate :3  )

That’s the difference between prescriptive and descriptive.

Think about it it with food:
What do guidebooks say people eat in your country?​​​​​​​  Look around you, what do people really eat?
What’s your national descriptive diet?

Think about it with language:
How are you supposed to speak your language?  What do people really say?
What do your grammar books say about English rules?
Do people follow the rules in movies? on Youtube? on Believe English? 😉