As I'm going deeper into level design analysis, I realize that there should be a sort of "contract" between the level designer (hereafter denoted "I") and the player (hereafter denoted "you"). Something that will at least feature the following items:
Art. 1°: I will not tease you with collectibles that are impossible to collect.Art. 2°: Whenever you will die, you will know that it was your fault.Art. 3°: I will not put you in a situation where the only way to keep on playing is to die.I'm afraid we can't do that.Many earlier games infringe those rules, at least partly. Whoever has played Commander Keen IV has at some point wondered how one could collect all those 1-UPs in the deepness of the lifewater Oasis... or that impossible-to-grab diamond at the end of Level 2 in GGS.
When you do observe art. 1° of the contract, however, placing an item somewhere that looks out of reach can be perceived as the signal that the player is missing some nuance in the gameplay mechanics. This happened in Donkey Kong Country, but I wasn't aware of the contract before I forced my way through the lost levels of DKC2 and discovered the roll-jump move.

Yes, you can!
It happened to me when playing Giana: Twisted dreams. There are two modes in that game: punk or cute. The punk Giana can DASH (even mid-air) and the cute Giana can HOVER. Let me call "TWIST" the mechanic that switch between punk and cute.

Black Forest did merge both TWIST and DASH mech...