Games

Absolutely this.

If we're going to take a Metroidvania as an example of this lesson, let's take Environmental Station Alpha. The game has a ton of potential as a good Metroidvania that is buried in a thick armor of speedrunner-level difficulty. I have never seen a Metroidvania be so stingy about health tanks, and this game desperately needs all of the health tanks you can get. It stinks of a developer team playtesting the hell out of their own game, and making difficulty decisions based on years of their own self-testing experience.

When you release a game with a Normal difficulty, no Hard difficulty, and then are forced to create a Easy difficulty after release, you know you've fucked up.

Here's how you do it: You can playtest your own game, but that one gets the "Hard" label. If you playtest for a Normal difficulty and you can't imagine how to create a Hard difficulty, the difficulty range is completely off. And Hard doesn't mean "only people in the double-digits can beat it". That's not even a scale, or just reserve that for some "Impossible" difficulty, if you want to get to 5-6 levels, like Doom does.

Normal should be some reasonable setting based on how others playtest the game. Get some expectations from your playtest audience in terms of the kinds of games they've played and beat before. Are they complete noobs to any sort of fast-paced gameplay, or have they beaten other Metroidvanias or games like Cuphead? Based on that, figure out whether the advice they give you applies to an Easy or Normal difficulty curve.