Artificial Difficulty

[Reynhart]

Following the "Trial and error is artificial difficulty" reasoning, Super Meat Boy or Dustforce would be mainly artificially difficult since they don't provide you with all information regarding the stage, the hazards and timings within, leaving the player to have to fail in order to gain information.

I haven't played SMB of DF, so I can only judge by what I see on videos. In SMB, you can clearly see the hazard. Every stage properly displays the chainsaws in your path, and it's your responsibility to memorize their pattern to reach your goal.

"Trial and error" is not "Failing until you manage to win", it's "Having to fall into every trap until you memorize what they are".
A good example of this is "I Wanna Be The Guy". First screen, you will die to the first cherry falling down on you before you even know it can kill you. When you manage to dodge all the cherries falling, you get on the first platform and you will die to the first cherry falling UP on you. And others screens are the same, you'll only know a trap is there because you died once to it.
And, far earlier, you had "Rick Dangerous" (Damn, I'm old ) for doing the same thing. "Two exact same ladders ? Pick one ! Too bad, this one is a trap, you're dead."

As for T9, it's exactly the same. You'll only know that you need to put meteors apart from each other after your first wipe on that. And since early fights end the first phase with 9 meteors (3 Red, 3 Yellow, 3 Green), chances are you will wipe. For the golem phase, you can do it on first try, since it can be natural to keep them apart. Phase 3, Heavensfall will kill most of your party, since you don't even know that it will knocback, you. The first Garrote Twist will also kill you. Etc, etc...

Now, let's look at Titan Hard. Phase 1, you have Landslide. First, you can dodge it with quick reflex, but even if you fail, the knockback can't kill you and the damage probably won't if your healer play it safe. Now, you know that this attack push you, so that's it's really important to dodge. Transition to phase 2, you can't fall directly when the surrounding shatters, since there's still a ledge. Ok, so now you know that Geocrush destroys the edge of the arena, and you'll be focused on subsequent jumps. In phase 3, you have the first set of bombs, but still a lot of safe space so that you can see how the explosion occurs, etc, etc...
For that, I think Titan is a much more "fair" difficulty, and that didn't prevent it from being a real pain in 2.0.

It's the same for Leviathan, you'll know that Body Slam moves you far before it can be a deadly mechanic...well except that it's only deadly in Extreme

[Eisenhower]

<examples from IWBTG, RD, T9>

Trial and error is a fundamental way of getting information and solving a problem. It's nice that you've brought up more examples, but in the end TnE is different from what constitutes the main chunk of difficulty in the examples. In DMB/DF, the biggest thing stopping a player from completing a level lies in timing the jumps and interactions (the same would be true for IWBTG). The player being forced to test and fail does not make the challenge more difficult, it only increases the time requirement. In these three examples the gathering of information doesn't break game flow either since the levels can be tested and reset comfortably, which is arguably much more important.

In progression, dying to meteors being too close for the first time in T9 or blackfire/whitefire in T12 does not break game flow. You (and everyone else) die within moments and then the party is back on their feet with the encounter reset and ready to be tested again soon thereafter. Trial and error is needed to gather information and more time is needed to solve the puzzle with this information. The trial and error component acts as a way to limit the flow of information. The challenge/difficulty lies in solving the puzzle with that information and the moving and using skills at the right time.

Trial and error methodology does not affect the difficulty of a challenge, but if the methodology breaks game flow the game becomes more frustrating to play.

For that, I think Titan is a much more "fair" difficulty

An interesting point. Let's compare Titan NM, Titan HM and Titan EX. These three encounters have almost the same basic components in the form of Tumult (AoE damage), Landslide (AoE knockback, area denial), WotL (AoE damage, area denial), Granite Gaol (resource denial). In HM and EX more AoE damage, area denial and knockback is added in the form of new abilities. In EX the adds provide additional area denial and knockback and the Granite Gaols also force positioning.

What is more interesting to note however, is that as we move up in "difficulty" it appears that the positive feedback loop regarding failure becomes stronger. Abilities will take a larger proportion of resources (health/mana) to deal with (assuming appropriate iL), and failures lead to more failures at a quicker pace due to the increasing limits on time to deal with them and time to recover. At the highest level of content in FFXIV this feedback loop is very, very strong.

When moving into raid content, the loop is at times so strong that the recovery window in terms of time or resources becomes so small that many players cannot catch it without outgearing the content. Whilst progressing such content with intended gear the strength of the loop is probably what makes players deem difficulty as "fair" or not.

[Reynhart]

In DMB/DF, the biggest thing stopping a player from completing a level lies in timing the jumps and interactions (the same would be true for IWBTG). The player being forced to test and fail does not make the challenge more difficult, it only increases the time requirement.

But in SMB or DF, you're not forced to "test" the wrong thing. If you have to reach a door, you'll have lava and chainsaws on your way, and you'll need to time your jumps to overcome these hazards. In a pure "trial and error", you'd have two doors in front of you, and you'll have to guess which one is the right door without any hint (And the wrong will kill you )
Of course, no games relies only on "trial and error" mechanics, or it would be blatantly obvious that no skill is required.

In progression, dying to meteors being too close for the first time in T9 or blackfire/whitefire in T12 does not break game flow.

This is something else altogether. Breaking the game flow is not a part of difficulty but longevity. In FFXI, if the whole party wiped in an arena, regardless of difficulty, everyone would have to go to their home point and crawl all the way back to the arena.

Trial and error is needed to gather information and more time is needed to solve the puzzle with this information.

The problem is when the only way to gather information is by failing. Blighted bouquet is really the biggest offender here...I really wonder how the first people found the trick...

An interesting point. Let's compare Titan NM, Titan HM and Titan EX.

Remember that you can't do a stronger Titan without having doner the weaker one. This means that Titan NM provides informations for HM, and HM for EX. So when EX come, the game can be quite brutal in its mechanic since you know how to deal with deal. Now you only have to do it with more stress and less ressources (comparatively)

When moving into raid content, the loop is at times so strong that the recovery window in terms of time or resources becomes so small that many players cannot catch it without outgearing the content. Whilst progressing such content with intended gear the strength of the loop is probably what makes players deem difficulty as "fair" or not.

Raids are the only content where you face one-hit kill mechanic without any prior experience. Even more, the game "tricks" you by using the same almost the same mechahnics with a slight change. For example, when you see the green crosshair mark on you, does the dive occur where you stand at the moment it appears or at the moment it dissapears ?

EDIT : There IS the game that only relies on trial and error !
DRAGON'S LAIR !

[Eisenhower]

(a) But in SMB or DF, you're not forced to "test" the wrong thing [...]

(b) This is something else altogether. Breaking the game flow [...]

(c) [Regarding Titan]

(a) A stage SMB/DF can in many cases not be solved through insight or theoretically (and then apply a solution) as the game does not provide complete information regarding said stage or special mechanics when first encountered. In addition for human players, that player must test various parts of the game (jump timing, path) to reach a solution.

Again - your example of a "pure trial and error" game would not be a difficult one, merely an exercise in patience.

(b) That quote feels out of context. Game flow was mentioned to note that gameplay that involved trial and error where error led to a failure state are not inherently detrimental to an experience. I made no correlation between game flow and difficulty.

Solving Blighted Bouquet wouldn't have taken too many tries. First time seeing BB cast, someone stuns/silences/pushes and the tank pops mitigation but everyone dies. We know we can't interrupt it and that it hits everyone. When BB is first used, there are only briar patches in the arena and no adds, so you might try to have the boss on it or stand on it to mitigate the mechanic but everyone dies. Or you'd try standing far away or under the boss but everyone dies. But some of the attempted solutions will involve a player not doing anything (such as a melee DPS at max range waiting for the cast) and that player survives. Now there's a partial solution to the puzzle. Since BB is cast around 70% and the initial burn of the boss is quick, the process of reaching BB and testing it isn't very tedious.

(c) The Titan example was mainly to highlight the failure feedback loop and what is perceived as fair difficulty. That aside, I get the impression that there are a multitude of one-hit kill mechanics outside of raid encounters. But I'm wary. Please detail what your definition of a "one-hit kill mechanic" is.

As for Dragon's Lair, are there not times in the game where observation and deduction can provide the player with the correct answer without blindly attempting all solutions?