Newer players have a tendency to not make enough items early, and instead greed for BIS (Best in Slot). Kenobi presents two different situations while explaining what you should make and why.

Situation 1

You have the following board and your components are Bow, Belt, and Tear.

If you play Kai’Sa LW is mandatory. Since you already have a bow, look for Glove on 1st carousel. It’ll take too long to get BB & Morello for Teemo. Instead make a tank item (Redemption) with your available components.

Situation 2

It’s later game and you still don’t have antiheal. Your items are Tear, Belt, and Cloak.

Creating Redemption would be a strong defensive item for Galio, but then it would be difficult to find/make Morello once the belt is used. Slam Adaptive Helm instead.

Link to Kenobi’s original post