No Self-Buffs

""Fun fact about Voodoo, Larry...can't conjure a thing for myself.""

- Doctor Facilier, The Princess and The Frog

Strangely often, the magician, witch, wizard, cleric, Evil Sorcerer, Mad Scientist, support class, etc. have the ability to bestow strange and amazing transformations, alterations, powers and buffs on other people, for whichever reason, but are unable to use their amazing powers to directly benefit themselves. Though rather thematic, it doesn't seem to be directly mentioned in most Fairy Tales and mythologies, even when it is implied.

Nevertheless, this is almost a necessity for both a plot device and a video game balancing mechanic, and for the same reason: It means the enchanter/caster/Defender/whatever requires other people to move things along, and prevents him from making everything trivial with his own power.

Exceptions can result in a very powerful character; see Co D Zilla for an example of why this may be a balance requirement.

Literature

 * In the book The Candy Shop War, magicians can't usually use their magic on themselves for a number of reasons. The most prominent is that magic works better on the young, and by the time you're old enough to understand magic, you're not a kid anymore.
 * In the Discworld novel Sourcery, it was mentioned that the only thing the wizards couldn't magically improve- even after they started recieving power from the Sourcerer- was themselves (or at least, not for more than a few seconds).
 * In the Spellsong Cycle, magicians cannot cast magic on themselves. They can, however, cast magic on each other.
 * In Patricia C Wrede's Enchanted Forest Chronicles, Herbert can spin straw into gold for other people, not himself.
 * In The Wheel of Time series the Aes Sedai can not use their powers (mostly Healing) on themselves. This is explained by the magic needing to "weaved" and "applied" to someone. In this way its impossible to to lay a weave upon yourself as you would be unable to properly see it. It's a pity they couldn't use mirrors or bend light or something to get around that ... other than that, it's a pretty consistent rule: there's an anecdote about an Aes Sedai whose mental block (Wilders often acquire these when learning to keep a lid on their powers on their own) was that she couldn't touch the Source with her eyes open. Naturally, this made her rather ineffective.

Comic Books

 * The deformed mutant Masque, from the Marvel Universe, has the power to alter anyone's facial features, save for the own.

Tabletop RPG

 * In early editions of Dungeons and Dragons, some monsters (archdevils, efreeti and noble djinn) could grant another character's wishes, but not wish for things themselves.

Video Games

 * War Craft 3 has Holy Light and Death Coil, very powerful healing spells which can only be used on other units. (Though to compensate, the Paladin can become invulnerable and the Death Knight can absorb the health of a nearby friendly unit.) Some spells also don't work on the caster (but do if from another caster) like Invisibility and Anti-Magic Shell.
 * Mostly averted in World of Warcraft, any spell which can buff a target can buff the caster (indeed some default to buffing the caster if there is no target).
 * A few exceptions exist where the caster can only cast a buff on someone else, but the effects of the buff also benefit the caster. One example would be Focus Magic, which increases the target's Critical Hit chance by 3%, and when they score one increases your own. A fairly common variant is a spell cast on the casters minion by default that directly or indirectly benefits the caster as well.
 * With the introduction of Deathknights, Death Coil returns as a spell that can be used to damage enemies or heal friendly undead, most commonly the Deathknights Ghoul minion. However, they can temporarily become undead themselves and use this spell to heal themselves.
 * City of Heroes naturally has the support powersets mainly only able to buff others, though some can also buff themselves; sometimes while debuffing or damaging enemies in the process, sometimes in a power that affects all of their teammates, including themselves. The reasons for this are obvious; even two buffers looking after each other can be a very effective team.
 * In Team Fortress 2, while the Medic can't heal or buff himself with his Medigun, doing so still boosts his own regeneration rate; additionally, when Ubered, both himself and his Uber target(s) are invincible.
 * Very slightly averted with the Kritzkrieg, which allows the Medic to heal himself with the taunt, although it's much slower than the usual healing rate and leaves him wide open to attacks. However, its Ubercharge effect is completely No Self-Buffs since the medic cannot take advantage of it.
 * The Engineer benefits less from his dispenser than other classes, as metal generation is limited while ammo is not, even though the two are interchangeable when it comes to picking up dropped weapons and ammo boxes.
 * In Shadow Hearts Covenant, Lucia's oils will affect the three other party members but not her. In Shadow Hearts: From The New World, Ricardo's songs work the same way.
 * In Final Fantasy VI, Sabin can use his "Mantra" and "Spiraler" Blitzes to heal his teammates, but not himself (using Spiraler actually kills him).
 * Flonne has a skill named "Power of Love", which recovers the HP of her allies, but not her own.
 * Other spells in the game can be cast on anyone of the player's choosing.
 * Pokémon Black and White introduces Heal Pulse, which heals a target other than the user. It's made for double battles.
 * Which does nothing to abate the guilt when a wild Audino spams it on you while you're beating the crap out of the poor thing for precious EXP.
 * In Mini Robot Wars, the Fixer Bot can heal all minirobot units around her, but not herself.
 * In zOMG!, the strongest and most stamina-effective heal is Wish... which can't be used on the user. Previously, this was also the case with Rock Armor, which has since been changed.

Western Animation

 * The witch doctor Facilier in The Princess and The Frog mentions this as a reason he has to work his schemes through others.
 * In Aladdin and its sequels/spin-off TV series, the Genie's power is much greater when granting wishes for others than when doing things for himself. The former lets him wield "super-phenomenal cosmic power", while the latter only lets him use "semi-phenomenal nearly-cosmic power."