Fail

Certain Assassin attacks have prerequisites to work. If these are not met, the attack will result in a fail (as opposed to a miss or block).

A fail can also mean when a spell is cast but the target dies while casting, or when a spell like Spell Breaker causes it to fail. The spell will still cost the normal amount of energy and cause exhaustion if it would normally do so, but it will not start casting (Note that Glyph of Lesser Energy will prevent you from losing at least some of the energy, but because it will not be used up). Note that a skill like Obsidian Flesh will prevent someone from being the target of a spell, which is different. The spell will not start casting and therefore no energy will be lost.