People get angry about 'grammar' on the internet. To the extent that memes have sprung up about it.
The scare quotes around 'grammar' are because most of what passes for grammar mistakes are really nothing of the sort. I work with foreign students, helping them get up to speed with English for university courses in the UK. They make real grammar mistakes. Here's an example of what someone without a firm grasp of English grammar sounds like:
'She have no much friend.'
Any one who has taught EFL will tell you that this isn't all that bad either. Learners can come up with some quite impressively bad sentences. At least with this one we can sort of guess of guess what the person is trying to say. That's why I think it's wrong to call something like 'your/you're' a 'grammar' mistake. Native speakers are very unlikely to make what could legitimately be called a 'grammar mistake'. More often than not they are spelling mistakes due to homophones like 'they're/their/there' or 'too/to'. The person knows what they want to say but they don't know how to spell it. Even the cringe inducing 'could of' is a misspelling. In rapid speech 'have' preceded by a consonant (the d of could) will almost always lose its 'h'. Sometimes we'll write this as could've. The problem is that the sounds of 've' /əv/ and 'of' /əv/ are identical. So again, we see homophones causing spelling mistakes.
How do I know that Native speakers are not making 'grammar' mistakes? Consider the following sentence:
She doesn't have many friends.
How many grammar rules are in this sentence? In fact there are numerous rules here all of which native speakers manage to observe almost all the time without any problems whatsoever - a feat quite beyond most of my students -even those at quite high levels of proficiency. Hold on, this is going to get complicated.
First the sentence is arranged subject verb object like most English sentences. In Japanese it would be subject object verb as in 'she many friends doesn't have'. Next there is the fact that the object 'friends' is plural. So the noun has an 's' on the end. It's quite amazing that we don't get this wrong since it's so small and fiddly and also because English has a huge number of irregular plurals (dog dogs, potato potatoes, child children, party parties, mouse, mice, men man, fish fish, wife wives, ox, oxen, datum, data, bus buses, passer-by passers-by, index indices, octopus octopods). The writer also knows that as 'friend' is a countable noun (unlike say rice or coffee) we not only have to add an 's' but we also have to use the word 'many' not 'much'.
I told you this was complicated.
The native speaker also effortlessly manages this most complex of verb situations. the main verb is 'have' but as we are using 3rd person 'she' it changes to 'has'. However that's not all, as we're using the negative 'not' we need to add 'do support'. Did you know English is one of the only languages to have do support on the planet? Of about 6,000 languages around now, there are only about three with do support and you can speak one of them. You lucky thing!
Back to the sentence. So we're in the middle of negating the verb and you'll notice that all of the verb information has moved from the 'have' to the vampiric 'do' which has become 'does'. The negative marker 'not' has reduced and been sucked in by the 'do' as well. All bow down to the mighty 'do'.
So there you have it, three paragraphs to describe five words. All of the information I've described about English grammar is contained in a native speaker's head and flows out effortlessly when they speak. In fact, most of them probably couldn't describe these rules if asked. Sure, some variations may exist ('she don't have many friends') but even these are regular and systematic. That is, no one says 'She have don't many friends' as a matter of course. If anything the 'she don't' is a more regular and logical version (but let's not get into that one).
As Atkinson notes, every native speaker knows more grammar rules than any grammarian has ever been able to codify. Your command of the intricacies of English grammar is so vast and complex it has not yet been fully recorded. Instead of celebrating this incredible fact we get upset when someone spells a word incorrectly and wonder if they don't understand 'grammar' and perhaps if they're stupid. It's a funny old world.