Fear is a mental attack and a magic attack which depends on enemy mdef. You can enchant it for time (or was it cost, I forgot) to increase the duration significantly. The reason it actually lands on stacked people is because all debuffs in HIGH5 have a hardcoded minimum of 10% chance and maximum of 90% chance. This means even frost bold can land on someone with hero aegis, full buffs and epics even if it only lasts 1 second... The only exception to this are the absolute debuffs (real target from trickster and stigma from SE). These will never fail unless the target has tMystic immunity from PP.
Cancel (and steal divinity) never fail, only the amount of taken buffs can be decreased by things like angelic icon(?), lion heart, arcane protection, etc. Cancel taks up to 5 buffs at once, steal divinity is up to 7. Note that it's possible to resist every single buff being taken if you have extreme resistances, but this will not happen often.
Disarm is not a mental attack (so epics, mental shield etc do nothing about it). The only thing that affects disarm landing are general debuff protection (like arcane protection/chant of spirit (?)) and the target's STR value. Warriors such as gladis and tyrants are noticeably harder to disarm than mages with -10 str dyes. This applies to both doombringer's disarm and gladi's weapon blockade.