Note: This is a repost of a previous post. Blogger is unwilling to allow me to edit the older version into a readable format, so I've decided to create a new version. Sorry for the inconvenience.
Selecting mechanical perks can be one of the most satisfying aspects of the number crunching of character creation. Most modern systems have feats, extras, perks, or an equivalent mechanic that lets you give your character an extra boost at the table. These abilities are thrilling because, unlike attributes or skills, you may be the only one with a certain perk. This is exciting! You're the *only one* who can fly fighter planes. You're the *only one* who gets to roll 12 siders for long sword damage. You're the *only one* who can't be surprised in combat.
This uniqueness can be exciting for a game designer, but it can also be a pitfall, and here's why: By creating a perk that says "You can do X, Y, or Z," you are making it clear that a character cannot do X, Y, or Z without the perk. This can lead to dangerous situations at the table where a GM is caught between two of the "rules" that many GMs strive to obey. On the one hand, telling a player, "Yes, you can fly a fighter plane in this situation even though you don't have the Fighter Pilot perks," can be a stab in the back for a player who did take the perk. At best, it's a slippery slope toward another situation where some other player at the table *will* have the perk in question. ("But you let John justify flying a fighter plane without the fighter plane skill!")
On the other hand, telling a player no violates "the rule of cool.*" "Since my character was raised by hunter-gatherers in the Forgotten Forest, he should be able to track someone using the survival skill, even though I didn't take the stunt." This kind of statement may be extreme, but this sort of thing makes sense sometimes. For instance, if a player decides to leap from the balcony and attack, but doesn't have the "leap attack" perk, how can you justify saying no?
While this is really an issue that comes up at the table, smart design should dodge some problems. When you're designing perks for your game, (and I do recommend perks; they're fun!) never create a perk that says: "With this perk you can do X." Instead, phrase your perk like this: "With this perk you can always do X and you get Y bonus." Not "With this perk you can wield exotic weapons," but "With this perk you can wield exotic weapons and you get a +1 bonus with the weapon of your choice." Not "You can fly fighter planes," but "You can fly fighter planes and receive 2 bonus dice of dog-fighting rolls." Not "You can roll survival in place of investigation to track someone through the forest," but "You can roll survival in place of investigation to track someone through the wild and receive a +2 bonus to this roll in the environment of your choice.
*For those unfamiliar, the rule of cool states that if a player says they want to do something, and it's cool, you should just let them do it.