Every generation rediscovers the argument: a game with no checkpoints is either bold or cruel. An only up game sits entirely on the bold side of that line, and the reason it works is not stubbornness — it is what the absence of checkpoints does to how you pay attention.
Checkpoints quietly tell you which parts do not matter. Everything before the flag becomes skippable filler your hands do on autopilot. Remove the checkpoint and every section regains weight: the boring ledge is now part of the same continuous risk as the hard jump, and — unexpectedly — the game becomes less frustrating, not more, because there are no fake progress resets. You never lose a checkpoint to a bug or a misjudge; you lose exactly the altitude you physically lost, and nothing else. When you play only up in this regime, your relationship with the tower turns honest: progress is real or it is not there at all.
The design also builds a specific kind of memory. Because you re-climb after every fall, sections get burned in not through repetition by choice but through consequence — you know the tower the way you know a commute. Plenty of modern games are praised for respecting the player's time. This one respects the player's attention instead, which is rarer, and once you have climbed a tower that never saves, going back to checkpoint flags feels like being read a bedtime story you already know the end of.
The honest counterargument is emotional: without checkpoints there is nothing to catch you, and some players simply play better with a net. If that is you, the compromise is a mental checkpoint — a section boundary you have named and promised yourself to reach before judging the session. It is not the same as a save file, but it gives the stubborn human brain a stake of its own, and the tower does not mind being climbed in promises.