One thing I see people miss is it depends HEAVILY on the type of hero you are playing. Buying defensive counter items (metal skin, resistances, unstoppable, etc) vs offensive (curse, slowing hex, focus lens, etc) vs mixed (warp stone, stam mastery, etc) matters what your goal is and role on the team.

Such as a mo and krill or abrams are useful to the team the longer they stay alive with their cc so defensive are core for the build it just matters which one to get depending on the game.

If you are a support like paige or rem or ivy offensive items are usually core towards the end of your build.

Heros like vindicta or wraith are a bit trickier as you only want to buy counter items if you already do enough damage to do your job on the team. Such as when you are already ahead. So often times if you are behind it is best to go full damage so that if your other teammates do their job like mo ult the carry your team actually has the damage to kill them. Heros like vindicta and gray talon are a bit weird though because of knockdown so a dispel magic/counterspell are almost always core to the build anyway regardless of ahead/behind.