Since the article was written prior to the invention of automatic spelling correction, these sorts of seemingly trivial errors could tarnish one's first impression significantly. If you know nearly nothing about someone but need to form an opinion of them, you will use everything you do know to assess them, regardless of how trivial. Furthermore, you will generally be biased towards criteria that are more difficult to fake. It may not be fair but it's how humanity works, and being aware of this can help you greatly.

Confidence, intelligence, credentials, and experience can be faked or lied about. Comparing someone's written words with their speech, in person or over the phone, will give you a more reliable picture of how they think and communicate than anything else.

I agree, it was more of a non humorous joke.

Reading this article is almost in perfect timing with my situation. I am 24 year old with only 2 years of college. I was learning more outside of school than in. Even though I might not be the best developer or maybe not even average, I took the jump in trying to make it. So far so good. With learning that experience is everything and know how to get help will take you far. I feel like I know twice as much as I did last year. Is it possible that a lot of us are trying to reach that feeling of accomplishment?

I most certainly pass this article on to friends and peers.

Do keep in mind that this letter (essay?) was written in an era when SMS wasn't a thing and getting an education involved (quite literally) crossing your t's and dotting your i's. A keyboard wasn't a thing yet and spell check was something witches and wizards did before their exams.

Things have gotten speedier, and yet, much lazier now - so much that we have begun to rely a fair bit on technology and a common shared understanding of the concepts that unite us into the communities we partake in. Add to that, the exchange of cultures via this great, big melting pot called the internet, and you get a hodge-podge of words, symbols and grammar that we end up loosely calling a language. As with all melting pots, the contents of this one have melded into each other so much that these changes to the contents have (again, literally) stuck!

TL;DR - It was different back then & it certainly is much different now. It really doesn't matter what words (or spellings) you choose; what matters is the thoughts you are trying to convey through your words (and spellings).

Ah yes, the school of thought that supposes the ability to distinguish between "your" and "you're" is the essence of intelligence.

That's not what the author is saying. He's saying that if you are either unable or unwilling to correctly use "your" and "you're", you are probably unable or unwilling to pay attention to the details that matter to success in his business. I agree that there's a fine line between proper attention to detail and nitpicking, but taking the author's statement in context I don't think he's on the wrong side of it.

It makes sense, but that's the danger of it in my opinion.

If you think this way, it's worth going back and examining the writings of people you admired. You might be surprised! Or not.

It depends on why I admired the people. If I admired them for their success in business, then yes, I would expect their writing to show attention to details like spelling. But if I admired them for something else, I wouldn't necessarily expect that. I'm certainly not saying that anyone who is worth admiring has to spell correctly.

Not 'the essence of intelligence' but 'one indicator of self-discipline'.

Clear writing is a proxy for clear thinking.