User blog comment:Krufix/Last Whisper - When to get?/@comment-4743916-20121106060243

I usually have a general rule of thumb to consider building LW after I've gotten my major damage item (either BT or IE) and at least Zeal. After that I actually look at the enemy team's itemization and consider what to build. If I'm anywhere behind that Zeal, I don't even consider whether to build anything else because not building at least Zeal would put me considerably behind because of the mobility I'm missing out in.

Typically my general rule is if I see a complete armor item built on a Tank or any armor on the major squishies on the enemy team, I rush for LW. This is because at that point the tank's armor will be breaking 200 with just 1 armor item and the squishy would be breaking 100 armor with just a chain vest at that point of the game. If a tank has only chain vest and the squishies haven't built any armor, I wouldn't consider going for LW as it simply isn't that cost effective at that point.