Editing GURPS (section)

===Success rolls===
GURPS uses six-sided dice for all game mechanics. For instance, if the damage of a weapon says "3d+2" then you'd roll three six-sided dice, add the results of each die together, and add 2 to that result. Likewise, if it said "2d-1", you'd roll only two dice and subtract 1 from the total result. For stat and skill checks, the player always rolls three six-sided dice. Note that this makes a "default" skill check (a skill of 10, based on an unmodified attribute) 50% likely to succeed. 

Making stat and skill checks in GURPS is the reverse of the mechanics of most other RPGs, where the higher the total of the die roll, the better. GURPS players hope to roll as low as possible under the tested stat's rating or skill's level. If the roll is less than or equal to that number, the check succeeds. There is no "target number" or "difficulty rating" set by the Game Master, as would be the case in many other RPG systems. The GM may, however, calculate various modifiers to add or subtract to the die roll. In this way, positive modifiers increase the chance for success by adding to the stat or skill level you must roll under while negative modifiers deduct from it, making things more difficult. 

For example: a player makes a pickpocketing test for her character. The player has assigned a Pickpocket skill with a level of 11. Rolling 3 dice, the result must be 11 or less to succeed. If the player rolls above 11, then her character has failed the attempt at pickpocketing. No matter the level of the skill, a die roll of 18 or 17 is always a failure, and a roll of 3 or 4 is always a success. The Game Master may decide in such cases that, in first case, the character has failed miserably and caused something disastrous to happen or, in the other case, that she succeeds incredibly well and gains some benefit as a result.