What constitutes a fail

Crafting: you drop it, rip it to pieces or break it, burn it, etc.

Sneak and hide: nothing, people just see you which I find hilarious.

Ride: you get thrown on your ass, which I also find hilarious on a critical or your mount doesn't move.

Contact, barrier and expel: you just fail to do it but I feel like how much stun you lose also factors in.

Trample and Charge:your mount won't do it.

Direction sense: you go the wrong way.

Backstab: you make some kind of noise alerting the target.

Poison: if it's a blade, you cut yourself poisoning yourself. Also hilarious.

The common Way skills require that they be able to do their thing to get a skill up from. So contact needs something to actually contact.

Poison means you don't poison the object, or you poison yourself.

Backstab has a missed stab, and it has a 'target whirls around because you misstepped'.
I think the missed stab still gives you the first attack though?

Ride will now give little echos about how your mount isn't listening very well/being thrown/refuses to move.

Crafting things that have more then one end result are special in that if you don't get every last one it's a fail.

Bash you must have your bash dodged to fail. Being reversed doesn't do anything.
Kick you must have your kick dodged to fail. Being reversed doesn't do anything.
Disarm you must drop your weapon/fail to disarm. Being reversed gives a skill check to the other person.

Archery you need to miss.
Throw you need to miss.

Weapon skills require you to get dodged or parried.
Offense requires you to get dodged.
Shield use requires you to be hit while using a shield.
Parry requires you to be hit while using a weapon, and not a shield.
Defense requires you to be hit without a weapon or shield, unless don't have the parry skill.
Dual wield and two handed go up from missing/parried/bouncing off natural armor
Dualwield can go up from fighting unarmed, as long as you are attacking with the off-hand.
Weapon skills might go up bouncing off natural armor, but I haven't seen it to confirm it.

Flee needs you to panic or fail to cover yourself when you flee. You don't actually need to get hit though. If you block or parry the flee attacks, then it still counts.

Hunting and skinning are similar. They also go up very easily.
If you don't get every possible result, then it's a fail.

Blind fighting requires you to be attacked in darkness. You fail if you don't fight back.
It also raises in no visibility sandstorms, but I'm not really clear on how.

Hide is pass or fail when you do it. You don't really know unless you test it.

Sneak seems to require someone/something to sneak by to fail, or it's very very easy at the higher end. It always seems to take forever to max out.

Listen can go up anytime you fail to pick up conversation from a table/whisper/anotherroom/behind a door/someone sneaking.

Scan fails on not seeing something hidden. It does a check every time you look at a room with something hidden in it. So spam look at something hiding, and get a handful of checks/fails.

Sap is pretty much like backstab.

Pick is failing to pick a lock/breaking your lockpick

Value is failing to get the accurate numbers. It's actually a little hard to figure out unless you value something multiple times over a long period.

Haggle is when they refuse to change the price. If they ask to keep the same price, then I don't think it counts?

Search fails anytime you fail to find the hidden thing in a room with one.

Climb fails when you fail to go up/catch yourself from falling

Forage fails when you don't find anything at all.

steal fails when you don't steal anything. I forget all the little messages, and a critical fail will have the person calling for guards.

peek fails with not being able to see what's inside. I think that's it?

However, I can't see the code. So according to Nyr I couldn't know any of this.
This is only through observation and my own judgment.

ur wording here is all fucked up. r u saying that getting hit by a weapon or shield wont raise ur defense? r u saying that if ur holding a weapon or shield, that getting hit in that scenario wont raise ur defense?

i could totally make a skill progression system on mudlet wit deez lines but im lazy

That's how the code was programmed. The other thread has more details.

Using a shield, parry and defense won't raise. Have parry and using a weapon, defense won't raise. Using no weapon and no shield, defense will raise. I'm not sure if this is true. Forgot who said it.

This kind of makes sense. If you are using a shield and get hit you're shield use was what failed. Same if you have a weapon and didn't parry.