Now, this is probably the most low elo thing ever, but I need to get this off my chest. If you're facing a champion with huge in-combat sustain, or something with a supression, you are allowed to deviate from your core items to build GW or QSS or whatever. Because if you don't. The Regen champs and the supression champs are going to roll all over you.
OK? DO I NEED TO GO OVER ANYTHING?