> A thick desire is one that changes you in the process of pursuing it.
>
> A thin desire is one that doesn't.
>
> ...
>
> The person who checks their notifications is [a thin desire],
> afterward, exactly the same person who wanted to check their
> notifications five minutes ago.
[I added the brackets]
The author, I think, would label the desire for sugary drinks as a thin desire. However, that desire tends towards unfavorable consequences: mood swings, poor dental hygiene, weight gain. Thus it undermines one's body. This "changes you" -- for the worse, yielding a contradiction. If the preceding logical analysis is sound, the article's terms or argument are flawed.
The wording was very careful to say the pursuit of the desire changes you. That's very different than obtaining the desire changing you.
It's not a real remedy for your comment because we could probably come up with an example where the pursuit of the desire changes you in a bad way. For example, if you're a heroin addict and you're breaking into homes to steal things so that you can buy drugs. But I think it does help narrow the scope enough that the intent behind the statement becomes more clear.
There is something really interesting about people (which I think I'm borrowing from Atomic Habits by James Clear): Every time you take an action in service of a goal, it helps prove to yourself, a little at a time, that part of your identity involves pursuing that goal. For example, each time I spew out a journal entry or cobble together a blog post, it reinforces the belief "I am a writer."
With this in mind, it suggests a theory: doing the thing itself changes you. After some suitable time delay, perhaps. (This is how exercise adaptation works at least.)
But connecting this together still feels muddled. What is the difference between doing the thing and the consequences of doing the thing? The difference feels ... undefined? Maybe even arbitrary? All of this triggers my "inconsistency detectors" suggesting more thinking needs to be done.
Maybe the difference is that some actions provide certain emotional states while we're doing them: satisfaction, flow, meaning -- and this is what people mean by the first part ("doing the thing"). Maybe we can define consequences as the things that happen after we stop acting. Like the royalty checks that hypothetically will clog up my mailbox one day.
There's the motivation, the pursuit, and the achievement, and the consequences of each. I think it's fairly easy to tease apart the motivation and the pursuit, but you're focusing on a much more nuanced aspect of the action and its consequences. These really are tied strongly, but worth addressing individually.
As you point out, some actions are motivated and pursued because of the consequences of the achievement (writing a book or song, founding a company, being elected president). But others are intrinsically rewarding, which is usually shorter term.
You said it yourself - "sugary drinks... tend towards unfavorable consequences". The change happens as the outcome of the desire, not "in the process of the pursuing it".
The author, I think, would label the desire for sugary drinks as a thin desire. However, that desire tends towards unfavorable consequences: mood swings, poor dental hygiene, weight gain. Thus it undermines one's body. This "changes you" -- for the worse, yielding a contradiction. If the preceding logical analysis is sound, the article's terms or argument are flawed.