Opening the letter addressed to him, Eli “Hawk” Moskowitz smiled as he saw who it was from: the actor Jacob Bertrand, whom Eli had heard about more than once. Eli felt Jacob did an amazingly awesome job bringing him to life on Cobra Kai, and couldn't help smiling when he recalled an interview he’d found on YouTube with Jacob saying something like “I embody that darkness a little bit” in a sense.

To Eli from season one,
Stay strong. If you join the karate cult known as Cobra Kai, don’t get too sucked in, and don’t buy into it too much. But, you know, you might get a Mohawk and a back tattoo, as well as a girlfriend.

Unfortunately, much to your dismay, she’ll dump you after you’ve become the bully you strongly dislike and hurt your best friend and Binary Brother Demetri Alexopoulos by attempting to beat him up over his one-star Yelp review about the Cobra Kai dojo (which you had lost your head over), and at the mall of all places. Later, it’s pouring beer over his head at a party after he suggests a dose of inner peace, destroying his Earth Science project made out of Legos with a soccer ball, and then giving into the other Cobras when they pressure you into breaking his arm.

But one day, after all that (the last of which you’ll instantly regret doing because you really wanted to break something else), you’ll open your eyes and finally see the kind of person you’ve become, along with how you’ve been fighting on the wrong side the whole time. You’ll realize that Sensei Lawrence and Miguel had been right and Kreese’s methods were wrong and unhealthy; also, you’ll notice the other Cobras weren’t really your friends at all because they only knew you as Hawk, whereas Miguel and Demetri showed they were true friends because they knew you when you were Eli and still liked you anyway.

With that, besides deciding this is the final straw, you’ll believe you’ve now had it with both Cobra Kai and being the bully you strongly dislike. So, you do the right thing for once in a whole year by defecting from Cobra Kai in rescuing Demetri from getting his arm re-broken (since, deep down, you regret being the cause of said broken arm before) by first kicking away one Cobra, and then grab a shocked Doug Rickenberger around the neck before throwing him onto the glass table. (Of course, if you ever look back on that by imagining you’re watching it from afar, you’ll smile when you notice Doug was caught off-guard, because, obviously, he wasn’t expecting you to attack him instead.)

Then, you’ll turn to Demetri and give a sincerely honest apology for all the bullying you put him through before asking him if he wants to help you win “this thing.” (He will — trust me.)

Besides realizing you’d become the bully you’d strongly disliked, you’ll also finally see that deep down beneath the Hawk façade, you’d felt unhappy and lost without Demetri (as you’ve been best friends-slash-Binary Brothers since kindergarten), and you’ll even realize you’ve missed him as much as he’s missed you, and that your hunch about you both wanting each other and your friendship back is correct as well.

Finally, you’ll both fight alongside each other in taking down the other Cobras (using a variant of the wheel technique Sam and Robby used on you during the mall fight).

But although your decision to turn your back on Cobra Kai by switching sides and rescuing Demetri manages to do one good thing by rekindling the friendship between the both of you, it also results in Tory calling you and Miguel traitors for betraying Cobra Kai (although you and Miguel will do so for the right reasons). She’ll then turn to you and warn you to watch your back (as she’ll sense you’ve defected from Cobra Kai). Luckily, you’ll confidently return her glare back at her (as if to tell her she’d better take her own advice), while Demetri stands by your side and bravely tells her you won’t have to, as you’ve got friends watching your back for you.

I wish you all the best in life, and I hope you’ll think about what I’ve said here.
~Good luck,
Jacob Bertrand

After reading that last paragraph, Eli felt the urge to find Demetri and show him the letter he'd gotten. After all, Eli thought, Demetri and I are Binary Brothers, and I will never do anything to hurt him.

He felt sickened when he recalled what Jacob told him he was going to do in the letter (while simultaneously wondering how he could prevent it from happening). Trying to beat up their best friend over a Yelp review? Pouring beer over their head at a party after they suggest a dose of inner peace? Destroying their Earth Science project made out of Legos with a soccer ball? Giving into the Cobras when they pressure them into breaking said best friend's arm?

What kind of person hurts their best friend by doing things like that instead of showing positive qualities like comforting them when they’re having a bad day and being a good listener when they want to talk about whatever's on their mind?

He knew the answer to that one all too well. A bad person, or someone who knows they have a soul and a conscience, but never uses them.

He then made a solemn vow. Never will I become the bully I strongly dislike, and I will not do those things to Demetri either. After all, like Jacob said, if I did make that mistake, deep down, I definitely would feel unhappy and lost without Demetri; he’s literally the best friend anyone could ask for, and he still saw the good in me, even when I didn’t see it myself. In this case, I vow that if I ever do flip the script some day, I will also find a balance between Eli and Hawk by choosing to be the person who’s both nerdy and confident.

He nodded as if to convince himself with the last one. That’s what I should’ve done in the first place back when I had the blue Mohawk. If I’d gone for finding balance much sooner than later, Demetri and I wouldn’t have gone through that rough patch, I would’ve courageously stood up to the other Cobras when they tried to get me to break Demetri’s arm, and I would’ve given a surprised Tory a good telling-off by saying something like “Looks like I’d better watch my back, Princess” while giving her a smirk, much to her shock (because I’d take the words right out of her mouth).

While I did a complete 180 with the Mohawk and the back tattoo in order to distract others from my lip scar, Demetri made a vow to authentically be himself, which he did an awesomely cool job sticking with even after he joined Miyagi-Do and became a confident fighter over time. That, I well know, was a blessing in disguise for him, as he won the heart of Yasmine, the popular girl-turned-outcast, in the process.