How to get why an app crashed? I regularly obtain the infamously unhelpful "unfortunately crappyApp has stopped working". How to figure out what actually went wrong? I guess there's a stack trace somewhere, though ideally I'd like to modify the unhelpful message itself if that is possible on a rooted device.
You can simply see the crash stack trace after any crash happens.
Use ADB command below,

adb logcat -b crash #default
adb -d logcat -b crash #show from device when multiple device
adb -s logcat -b crash #show from simulator when multiple device