Celeste is one of the early frontrunners for best games of 2018 (early I know but our review says otherwise). The indie platformer is kind of like a mix of Pixel games like Cave Story and Kero Blaster with high-difficulty platformers like Super Meat Boy. But Designers at Matt Makes Games made a very conscious decision of fine-tuning difficulty for sake of the game's overall pacing as director Matt Thorson revealed in a reddit AMA about the difficulty grading throughout the game.
When asked by user "junkmail 22" whether the decision to make the visually complicated levels play easier than some of the more simpler looking levels was intentional, Thorson replied in the affirmative.
"This was deliberate - if a room is very hard to execute, I tend to make it easer to figure out and vice versa, otherwise it can start to feel impossible for a lot of people." This was because, as Thorson says, of the flow of the game. "Pacing is very important in the main story of Celeste because the feeling of the platforming has to mirror the narrative."
Thorson also cites the different kinds of challenges in Celeste that affect pacing, and should be taken into account while designing the game. Whether the difficulty is a result of a hard puzzle, a large area, or a portion that requires precise platforming.
While Celeste is certainly difficult, it's also very accessible. The game features a comprehensive Assist Mode which can be fine-tuned to best help you beat the game, without making it feel condescending or too easy. The assist mode is literally just that, an assist.
Either way, it's clear that the developers of Celeste poured a lot of attention into the difficulty of the game to make sure that the challenges, while great are ultimately surmountable. Which is just a testament to good game design really.