Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Here is the idea you can go toe to toe with anyone dealing huge damage while gaining lots of life allowing you to go for that half health tank with his buddy next to him. you get huge health bonuses from all the ad and ap bonuses with the 45% life steal you have after bloodthirster is maxed you don't really die... Unless you are ganked you must remember you are still not a tank and can be killed by getting spiked.