The handicap system is kind of an odd concept in some ways, as it's designed to measure a golfer's potential and not what they do on average. Your handicap is actually determined by the average of your 10 best indexes (this is measured by the slope and course rating at the courses you play and not just par in relation to your score) recorded during the last 20 scores posted. So basically, a guy who shoots 75 10 times and 85 10 times in his last 20 rounds will have a handicap in the 3 range, while a guy who shoots 80 for 20 consecutive rounds will be in the 8 range, that even though both guys' average score is 80. Now, that's not likely to happen often, but it serves as a decent example of how potential is the measure. It's also why "sandbaggers" don't post the low scores they shoot, because it has immense consequences on a handicap.