From the file's introduction
One of the more interesting innovations in the d20 system is the concept of Feats. While any two fighters or wizards will look more or less the same in class abilities and skills, it is their Feats that differentiate them. One fighter might use his Feat slots to become more skilled in mounted combat, while another might strive to be an excellent archer. Even at low levels, these two fighters will look and act very differently in combat.
In literature and popular culture, characters are often just as, if not more, defined by their faults than their abilities. Othello was gullible, and this enabled Iago to manipulate him. Han Solo was notable for his mercenary attitude. Captain Hook is remembered for... well, his hook. These faults, or drawbacks, lend color to the characters that have them. This d20 MasterKit product is designed to add these drawbacks to player characters.