Why 'am start PACKAGE' cannot launch some apps and shows an error? I keep having an error trying to start some apps using am start command. It works for many, but for some apps I get the same error mentioned below: 


#adb shell am start com.amazon.venezia
Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] pkg=com.amazon.venezia }
Error: Activity not started, unable to resolve Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 pkg=com.amazon.venezia }

#adb shell am start com.whatsapp
Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] pkg=com.whatsapp }
Error: Activity not started, unable to resolve Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 pkg=com.whatsapp }
use this:

adb shell am start -n com.whatsapp/.HomeActivity