This is something that I'm curious about. Every time I see mandatory secrets, I wonder what's the reasoning for its introduction instead of an every day door? Following that, if progression itself requires secret hunting mindset, what kind of mindset do the mappers demand from players for proper secret hunting? People like to use the "puzzle" excuse, but in reality it's neither a test of ingenuity or knowledge, more a patience test because you're punishing players for not looking at the right thing, and now they have to explore the whole area for hours on end to find that one tiny speck of different wall just to move forward.
Assuming of course, that the mapper would even provide the courtesy of having the path to progress use a slightly different texture to the rest of the wall surrounding it.
(Yes, I'm looking at you, Mordeth. A dozen locked doors that all look the same, a quarter of which opened by switches, with the one door that players have to use directly to open looking no different from the rest, is crime of the highest order.)
Players tend to have a specific mindset whenever they look for secrets. Searching for off-looking textures in a long line of walls, using walls that sit between torches or behind banners, doing leaps of faith to get to ledges that lead seemingly nowhere, hugging and using everything just incase they end up as fake walls or usable decor sprites that lead to supplies, backtracking whole maps 'cause that hidden switch they flick might open a wall on the opposite end, the works.
If progression itself forces secret hunting mindset, you'll end up with situations where players end up accidentally finding secrets instead of the way to progress, which frustrates more than it does satisfy, 'cause it's accidental. It stops being a reward for being attentive and watching for subtle clues, and instead is just another dead end in the search for the way to the exit.