Officially, GURPS stands for Generic Universal Role-Playing System. Unofficially, the ‘R’ stands for two things: Role and Roll. In GURPS world, we do our role-playing by roll-playing.
There are essentially two types of rolls that occur most often in GURPS: combat rolls and reaction rolls. Combat rolls are just what you think: you roll dice to determine success in combat. Reaction rolls are the rolls we make to determine success in a social interaction.
Both rolls usually use 3d6 and the margin of success is often applied to the results. This margin can be effectively increased with bonuses. For example, with ranged attacks you can wait and aim to improve your chances of hitting a target.
In combat, we describe the action and roll the dice to see if it succeeds. “I attack with my broadsword,” roll 3d6 and compare the result to your Broadsword skill. (You know how it goes from there.)
In social interactions requiring reaction rolls, we play out the encounter with the NPCs and roll to see whether the exchange was beneficial, detrimental, neutral, or whether it’s time to go into combat rounds. It’s not pure chance whether you succeed with a broadsword attack or a diplomatic encounter: high skill always increases the chance of success.
Additionally, almost every roll made in GURPS is subject to a bonus or penalty. Combat rolls may receive a bonus from certain advantages (such as Combat Reflexes and Striking ST), and there are a number of advantages that enhance social skills (for example, Appearance and Charisma). Skill rolls are usually affected by difficulty modifiers as well as time and effort.
With reaction rolls, bonuses not only accrue as the result of character traits but also the roleplaying of the player. An accomplished roleplayer may come up with an ingenious strategy to fast-talk an NPC and roleplay the exchange in such a way that the GM will award additional bonuses to the subsequent roll against Fast-Talk skill.
An additional thing to note about reaction rolls: in all other circumstances in a GURPS game where you’re called upon to roll 3d6, you want to roll low. Reaction rolls are exactly the opposite: the higher the roll on the part of the GM for the NPC reaction, the better the reaction. This makes life easier when considering modifiers that might be provided by a successful Diplomacy roll. If the Diplomacy roll succeeds by 4, the GM simply adds 4 to the NPC reaction roll. If the Diplomacy roll fails, the GM subtracts the margin as a penalty.
Obviously, adding the bonus increases the likelihood of a good reaction. That’s why it is good practice to always have at least one influence skill on your character sheet. Maybe your warrior isn’t very Diplomatic, and perhaps Fast-Talk is not honorable, but surely Intimidation is among his social strengths.
A number of roleplayers think the introduction of randomness inhibits their roleplaying. Their ability to portray a character doesn’t determine the outcome of events but merely influences the events. Often they object to having to “do math” by thinking about the bonuses and penalties involved with reaction rolls. They don’t like to find their behavior confined or constrained by a arithmetic.
Some GMs alleviate this burden by doing the math and sometimes the rolling itself. But this deters the player from understanding the underlying mechanics of their traits. Without that understanding, they will be unable to know how or when to use any possible bonuses or other benefits of their skills. The interaction of the dice mechanics and the player’s roleplaying talent are essential to a successful GURPS experience for both player and GM.
Say a player wants want to influence a security guard to allow after-hours access to a building. This is probably a fast-Talk roll, but Diplomacy or Intimidation could also be used. In either case, the GM should play out the scenario through interactive role-playing with the character and apply a bonus for the player’s performance. At the very least the GM should require the player to describe how nature of the influence attempt, the “angle” of the Fast-Talk or Diplomacy, the “how” of Intimidation with an armed guard. The GM should not simply allow a Fast-Talk roll with no input from the player; if the player refuses or is incapable of providing this, the GM should apply a penalty for a careless or unfocused attempt at influence. (And probably have an after-session talk with the player about role-playing and roll-playing.) Other scenarios are imaginable.
If you’re not going to do this, you’re giving up about half of what makes GURPS fun, and you’re decimating the power of the R. If you’re going to just sit around and let people roleplay without boundary and only call for dice rolls in combat, why play GURPS? If you aren’t going to award bonuses for good roleplaying, why not just play Munchkin?
Roll the dice and play the roll; play the role and roll the dice.