Sometimes, you find a great Expression online—or you come up with one yourself—and it’s perfect except it starts too early. You don’t want it to affect the layer until 3 seconds have past. Or you want it to hold off until a layer keyframe-animates to a certain location. Or you want it to wait until a layer’s scale reaches a specific percentage. In all of these cases, you need a trigger: some event that launches an Experssion when you’re ready for it to be launched.
Or maybe not. Once you get into Expressions, there’s always the risk you’ll start overthinking everything. So before I delve into the nitty-gritty of triggers, let me whisper two simple words into your ear: split layers.