This build maximizes Yi and his high AD. There is no focus on defense in this build besides the Greater Seals of Armor and Greater Glyphs of Magic Resist. It is an all out one man army Yi. Life Steal, Movement Speed, Critical Strike, Attack Speed, and Attack Damage are the strong points to focus on. Life Steal to keep Yi alive longer. Movement Speed to make up for his lack of range and keep the fight face to face. Critical Strike for more damage and to maximize Alpha Strike damage. Attack Speed to take advantage of his passive and high Attack Damage. Attack Damage to effectively use his Attack Speed and wipe out the competition fast before they can do anything. The masteries, items, and runes are built on these principals. Yi early game is a weak and fragile champion. This is why Jungling with Yi is the best option. His lack of range puts him at a disadvantage in lane. Jungle till ultimate is ready and then Have Some Fun!