Since you are trying to "adjust to reality and not stay in a bubble of naivete"... I'll be blunt. You are looking at it all wrong.
What exactly do you think marketing is? It encompasses everything from the logo on your business card to the elevator pitch you give. Marketing is simply a way of proactively informing people (the market) about something.
I'm assuming you are inquiring about this because you think marketing is unnecessary ("good products find buyers"), you think it's deceptive ("ads always lie"), or you've tried it and it wasn't successful.
Marketing is necessary if you want to guarantee success. Sure, you could get lucky, build something, and have everyone knock on your door. But that relies on luck, and luck isn't a business plan. If you want to build a business plan based on luck, then start buying lottery tickets: highest return with smallest investment.
As for deceptiveness, a job of marketing is to differentiate something from everything else. That means accentuating the good features and downplaying the bad. Everyone does that with everything, anyway.
Now if you've tried it and had no luck... that means you're doing something wrong. Marketing can be very successful, but it ain't easy.